chore: fix simproc doc-string

A user on Zulip [reported seeing an error code of "no
error"](https://leanprover.zulipchat.com/#narrow/stream/113488-general/topic/.60lake.20update.60.20broken.20on.20Windows.20.28.3F.29/near/429134334)
here.

.github/ISSUE_TEMPLATE/bug_report.md

@@ -33,7 +33,7 @@ assignees: ''
 
 ### Versions
 
-[Output of `lean --version` in the folder that the issue occured in]
+[Output of `#eval Lean.versionString` or of `lean --version` in the folder that the issue occured in]
 [OS version]
 
 ### Additional Information

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,14 +1,14 @@
-* [ ] Put an X in this bracket to confirm you have read the
-  [External Contribution Guidelines](https://github.com/leanprover/lean4/blob/master/doc/contributions.md).
+# Read this section before submitting
 
-* Please put the link to your `RFC` or `bug` issue here.
-  PRs missing this link will be marked as `missing RFC`.
+* Ensure your PR follows the [External Contribution Guidelines](https://github.com/leanprover/lean4/blob/master/CONTRIBUTING.md).
+* Please make sure the PR has excellent documentation and tests. If we label it `missing documentation` or `missing tests` then it needs fixing!
+* Include the link to your `RFC` or `bug` issue in the description.
+* If the issue does not already have approval from a developer, submit the PR as draft.
+* The PR title/description will become the commit message. Keep it up-to-date as the PR evolves.
+* If you rebase your PR onto `nightly-with-mathlib` then CI will test Mathlib against your PR.
+* You can manage the `awaiting-review`, `awaiting-author`, and `WIP` labels yourself, by writing a comment containing one of these labels on its own line.
+* Remove this section, up to and including the `---` before submitting.
 
-* If that issue does not already have approval from a developer,
-  please be sure to open this PR in "Draft" mode.
+---
 
-* Please make sure the PR has excellent documentation and tests.
-  If we label it `missing documentation` or `missing tests` then it needs fixing!
-
-* You can manage the `awaiting-review`, `awaiting-author`, and `WIP` labels
-  yourself, by writing a comment containing one of these labels on its own line.
+Closes #0000 (`RFC` or `bug` issue number fixed by this PR, if any)

.github/workflows/actionlint.yml

@@ -0,0 +1,22 @@
+name: Actionlint
+on:
+  push:
+    branches:
+      - 'master'
+    paths:
+      - '.github/**'
+  pull_request:
+    paths:
+      - '.github/**'
+  merge_group:
+
+jobs:
+  actionlint:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v3
+    - name: actionlint
+      uses: raven-actions/actionlint@v1
+      with:
+        pyflakes: false # we do not use python scripts

.github/workflows/changelog.yml

@@ -1,33 +0,0 @@
-name: add PR to changelog
-
-on:
-  # needs read/write GH token, do *not* execute arbitrary code from PR
-  pull_request_target:
-    types: [closed]
-
-jobs:
-  update-changelog:
-    if: |
-      github.event.pull_request.merged == true &&
-      contains(github.event.pull_request.labels.*.name, 'changelog') &&
-      github.base_ref == 'master'
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v3
-        with:
-          # needs sufficiently elevated token to override branch protection rules
-          token: ${{ secrets.PUSH_NIGHTLY_TOKEN }}
-      - name: Update changelog
-        run: |
-          set -euxo pipefail
-          escaped_link=$(sed -e 's/[\/&]/\\&/g' <<'EOF'
-          [${{ github.event.pull_request.title}}](${{ github.event.pull_request.html_url }})
-          EOF
-          )
-          # insert link below first dashes line (https://stackoverflow.com/a/9453461/161659)
-          sed -i "0,/^---*/s/^---*/\0\n\n* $escaped_link./" RELEASES.md
-          # commit as github-actions bot (https://github.com/orgs/community/discussions/26560#discussioncomment-3252339)
-          git config user.email "41898282+github-actions[bot]@users.noreply.github.com"
-          git config user.name "github-actions[bot]"
-          git commit -i RELEASES.md -m "doc: update changelog"
-          git push

.github/workflows/check-prelude.yml

@@ -0,0 +1,26 @@
+name: Check for modules that should use `prelude`
+
+on: [pull_request]
+
+jobs:
+  check-prelude:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          # the default is to use a virtual merge commit between the PR and master: just use the PR
+          ref: ${{ github.event.pull_request.head.sha }}
+          sparse-checkout: src/Lean
+      - name: Check Prelude
+        run: |
+          failed_files=""
+          while IFS= read -r -d '' file; do
+            if ! grep -q "^prelude$" "$file"; then
+              failed_files="$failed_files$file\n"
+            fi
+          done < <(find src/Lean -name '*.lean' -print0)
+          if [ -n "$failed_files" ]; then
+            echo -e "The following files should use 'prelude':\n$failed_files"
+            exit 1
+          fi

.github/workflows/ci.yml

@@ -6,8 +6,8 @@ on:
     tags:
       - '*'
   pull_request:
-    branches:
-      - master
+    types: [opened, synchronize, reopened, labeled]
+  merge_group:
   schedule:
     - cron: '0 7 * * *'  # 8AM CET/11PM PT
 
@@ -16,51 +16,204 @@ concurrency:
   cancel-in-progress: true
 
 jobs:
-  set-nightly:
+
+  # This job determines various settings for the following CI runs; see the `outputs` for details
+  configure:
     runs-on: ubuntu-latest
     outputs:
-      nightly: ${{ steps.set.outputs.nightly }}
+      # Should we run only a quick CI? Yes on a pull request without the full-ci label
+      quick: ${{ steps.set-quick.outputs.quick }}
+      # The build matrix, dynamically generated here
+      matrix: ${{ steps.set-matrix.outputs.result }}
+      # Should we make a nightly release? If so, this output contains the lean version string, else it is empty
+      nightly: ${{ steps.set-nightly.outputs.nightly }}
+      # Should this be the CI for a tagged release?
+      # Yes only if a tag is pushed to the `leanprover` repository, and the tag is "v" followed by a valid semver.
+      # It sets `set-release.outputs.RELEASE_TAG` to the tag
+      # and sets `set-release.outputs.{LEAN_VERSION_MAJOR,LEAN_VERSION_MINOR,LEAN_VERSION_PATCH,LEAN_SPECIAL_VERSION_DESC}`
+      # to the semver components parsed via regex.
+      LEAN_VERSION_MAJOR: ${{ steps.set-release.outputs.LEAN_VERSION_MAJOR }}
+      LEAN_VERSION_MINOR: ${{ steps.set-release.outputs.LEAN_VERSION_MINOR }}
+      LEAN_VERSION_PATCH: ${{ steps.set-release.outputs.LEAN_VERSION_PATCH }}
+      LEAN_SPECIAL_VERSION_DESC: ${{ steps.set-release.outputs.LEAN_SPECIAL_VERSION_DESC }}
+      RELEASE_TAG: ${{ steps.set-release.outputs.RELEASE_TAG }}
+
     steps:
+      - name: Run quick CI?
+        id: set-quick
+        env:
+          quick: ${{
+            github.event_name == 'pull_request' && !contains( github.event.pull_request.labels.*.name, 'full-ci')
+           }}
+        run: |
+          echo "quick=${{env.quick}}" >> "$GITHUB_OUTPUT"
+
+      - name: Configure build matrix
+        id: set-matrix
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const quick = ${{ steps.set-quick.outputs.quick }};
+            console.log(`quick: ${quick}`)
+            let matrix = [
+              {
+                // portable release build: use channel with older glibc (2.27)
+                "name": "Linux LLVM",
+                "os": "ubuntu-latest",
+                "release": false,
+                "quick": false,
+                "shell": "nix develop .#oldGlibc -c bash -euxo pipefail {0}",
+                "llvm-url": "https://github.com/leanprover/lean-llvm/releases/download/15.0.1/lean-llvm-x86_64-linux-gnu.tar.zst",
+                "prepare-llvm": "../script/prepare-llvm-linux.sh lean-llvm*",
+                "binary-check": "ldd -v",
+                // foreign code may be linked against more recent glibc
+                // reverse-ffi needs to be updated to link to LLVM libraries
+                "CTEST_OPTIONS": "-E 'foreign|leanlaketest_reverse-ffi'",
+                "CMAKE_OPTIONS": "-DLLVM=ON -DLLVM_CONFIG=${GITHUB_WORKSPACE}/build/llvm-host/bin/llvm-config"
+              },
+              {
+                "name": "Linux release",
+                "os": "ubuntu-latest",
+                "release": true,
+                "quick": true,
+                "shell": "nix develop .#oldGlibc -c bash -euxo pipefail {0}",
+                "llvm-url": "https://github.com/leanprover/lean-llvm/releases/download/15.0.1/lean-llvm-x86_64-linux-gnu.tar.zst",
+                "prepare-llvm": "../script/prepare-llvm-linux.sh lean-llvm*",
+                "binary-check": "ldd -v",
+                // foreign code may be linked against more recent glibc
+                "CTEST_OPTIONS": "-E 'foreign'"
+              },
+              {
+                "name": "Linux",
+                "os": "ubuntu-latest",
+                "check-stage3": true,
+                "test-speedcenter": true,
+                "quick": false,
+              },
+              {
+                "name": "Linux Debug",
+                "os": "ubuntu-latest",
+                "quick": false,
+                "CMAKE_OPTIONS": "-DCMAKE_BUILD_TYPE=Debug",
+                // exclude seriously slow tests
+                "CTEST_OPTIONS": "-E 'interactivetest|leanpkgtest|laketest|benchtest'"
+              },
+              // TODO: suddenly started failing in CI
+              /*{
+                "name": "Linux fsanitize",
+                "os": "ubuntu-latest",
+                "quick": false,
+                // turn off custom allocator & symbolic functions to make LSAN do its magic
+                "CMAKE_OPTIONS": "-DLEAN_EXTRA_CXX_FLAGS=-fsanitize=address,undefined -DLEANC_EXTRA_FLAGS='-fsanitize=address,undefined -fsanitize-link-c++-runtime' -DSMALL_ALLOCATOR=OFF -DBSYMBOLIC=OFF",
+                // exclude seriously slow/problematic tests (laketests crash)
+                "CTEST_OPTIONS": "-E 'interactivetest|leanpkgtest|laketest|benchtest'"
+              },*/
+              {
+                "name": "macOS",
+                "os": "macos-latest",
+                "release": true,
+                "quick": false,
+                "shell": "bash -euxo pipefail {0}",
+                "llvm-url": "https://github.com/leanprover/lean-llvm/releases/download/15.0.1/lean-llvm-x86_64-apple-darwin.tar.zst",
+                "prepare-llvm": "../script/prepare-llvm-macos.sh lean-llvm*",
+                "binary-check": "otool -L",
+                "tar": "gtar" // https://github.com/actions/runner-images/issues/2619
+              },
+              {
+                "name": "macOS aarch64",
+                "os": "macos-latest",
+                "release": true,
+                "quick": false,
+                "cross": true,
+                "cross_target": "aarch64-apple-darwin",
+                "shell": "bash -euxo pipefail {0}",
+                "CMAKE_OPTIONS": "-DUSE_GMP=OFF -DLEAN_INSTALL_SUFFIX=-darwin_aarch64",
+                "llvm-url": "https://github.com/leanprover/lean-llvm/releases/download/15.0.1/lean-llvm-aarch64-apple-darwin.tar.zst https://github.com/leanprover/lean-llvm/releases/download/15.0.1/lean-llvm-x86_64-apple-darwin.tar.zst",
+                "prepare-llvm": "../script/prepare-llvm-macos.sh lean-llvm-aarch64-* lean-llvm-x86_64-*",
+                "binary-check": "otool -L",
+                "tar": "gtar" // https://github.com/actions/runner-images/issues/2619
+              },
+              {
+                "name": "Windows",
+                "os": "windows-2022",
+                "release": true,
+                "quick": false,
+                "shell": "msys2 {0}",
+                "CMAKE_OPTIONS": "-G \"Unix Makefiles\" -DUSE_GMP=OFF",
+                // for reasons unknown, interactivetests are flaky on Windows
+                "CTEST_OPTIONS": "--repeat until-pass:2",
+                "llvm-url": "https://github.com/leanprover/lean-llvm/releases/download/15.0.1/lean-llvm-x86_64-w64-windows-gnu.tar.zst",
+                "prepare-llvm": "../script/prepare-llvm-mingw.sh lean-llvm*",
+                "binary-check": "ldd"
+              },
+              {
+                "name": "Linux aarch64",
+                "os": "ubuntu-latest",
+                "CMAKE_OPTIONS": "-DUSE_GMP=OFF -DLEAN_INSTALL_SUFFIX=-linux_aarch64",
+                "release": true,
+                "quick": false,
+                "cross": true,
+                "cross_target": "aarch64-unknown-linux-gnu",
+                "shell": "nix develop .#oldGlibcAArch -c bash -euxo pipefail {0}",
+                "llvm-url": "https://github.com/leanprover/lean-llvm/releases/download/15.0.1/lean-llvm-x86_64-linux-gnu.tar.zst https://github.com/leanprover/lean-llvm/releases/download/15.0.1/lean-llvm-aarch64-linux-gnu.tar.zst",
+                "prepare-llvm": "../script/prepare-llvm-linux.sh lean-llvm-aarch64-* lean-llvm-x86_64-*"
+              },
+              {
+                "name": "Linux 32bit",
+                "os": "ubuntu-latest",
+                // Use 32bit on stage0 and stage1 to keep oleans compatible
+                "CMAKE_OPTIONS": "-DSTAGE0_USE_GMP=OFF -DSTAGE0_LEAN_EXTRA_CXX_FLAGS='-m32' -DSTAGE0_LEANC_OPTS='-m32' -DSTAGE0_MMAP=OFF -DUSE_GMP=OFF -DLEAN_EXTRA_CXX_FLAGS='-m32' -DLEANC_OPTS='-m32' -DMMAP=OFF -DLEAN_INSTALL_SUFFIX=-linux_x86",
+                "cmultilib": true,
+                "release": true,
+                "quick": false,
+                "cross": true,
+                "shell": "bash -euxo pipefail {0}"
+              },
+              {
+                "name": "Web Assembly",
+                "os": "ubuntu-latest",
+                // Build a native 32bit binary in stage0 and use it to compile the oleans and the wasm build
+                "CMAKE_OPTIONS": "-DCMAKE_C_COMPILER_WORKS=1 -DSTAGE0_USE_GMP=OFF -DSTAGE0_LEAN_EXTRA_CXX_FLAGS='-m32' -DSTAGE0_LEANC_OPTS='-m32' -DSTAGE0_CMAKE_CXX_COMPILER=clang++ -DSTAGE0_CMAKE_C_COMPILER=clang -DSTAGE0_CMAKE_EXECUTABLE_SUFFIX=\"\" -DUSE_GMP=OFF -DMMAP=OFF -DSTAGE0_MMAP=OFF -DCMAKE_AR=../emsdk/emsdk-main/upstream/emscripten/emar -DCMAKE_TOOLCHAIN_FILE=../emsdk/emsdk-main/upstream/emscripten/cmake/Modules/Platform/Emscripten.cmake -DLEAN_INSTALL_SUFFIX=-linux_wasm32",
+                "wasm": true,
+                "cmultilib": true,
+                "release": true,
+                "quick": false,
+                "cross": true,
+                "shell": "bash -euxo pipefail {0}",
+                // Just a few selected tests because wasm is slow
+                "CTEST_OPTIONS": "-R \"leantest_1007\\.lean|leantest_Format\\.lean|leanruntest\\_1037.lean|leanruntest_ac_rfl\\.lean\""
+              }
+            ];
+            console.log(`matrix:\n${JSON.stringify(matrix, null, 2)}`)
+            if (quick) {
+              return matrix.filter((job) => job.quick)
+            } else {
+              return matrix
+            }
+
       - name: Checkout
         uses: actions/checkout@v3
         # don't schedule nightlies on forks
         if: github.event_name == 'schedule' && github.repository == 'leanprover/lean4'
       - name: Set Nightly
         if: github.event_name == 'schedule' && github.repository == 'leanprover/lean4'
-        id: set
+        id: set-nightly
         run: |
           if [[ -n '${{ secrets.PUSH_NIGHTLY_TOKEN }}' ]]; then
             git remote add nightly https://foo:'${{ secrets.PUSH_NIGHTLY_TOKEN }}'@github.com/${{ github.repository_owner }}/lean4-nightly.git
             git fetch nightly --tags
             LEAN_VERSION_STRING="nightly-$(date -u +%F)"
             # do nothing if commit already has a different tag
-            if [[ $(git name-rev --name-only --tags --no-undefined HEAD 2> /dev/null || echo $LEAN_VERSION_STRING) == $LEAN_VERSION_STRING ]]; then
-              echo "nightly=$LEAN_VERSION_STRING" >> $GITHUB_OUTPUT
+            if [[ "$(git name-rev --name-only --tags --no-undefined HEAD 2> /dev/null || echo "$LEAN_VERSION_STRING")" == "$LEAN_VERSION_STRING" ]]; then
+              echo "nightly=$LEAN_VERSION_STRING" >> "$GITHUB_OUTPUT"
             fi
           fi
 
-  # This job determines if this CI build is for a tagged release.
-  # It only runs when a tag is pushed to the `leanprover` repository.
-  # It sets `set-release.outputs.RELEASE_TAG` to the tag, if the tag is "v" followed by a valid semver,
-  # and sets `set-release.outputs.{LEAN_VERSION_MAJOR,LEAN_VERSION_MINOR,LEAN_VERSION_PATCH,LEAN_SPECIAL_VERSION_DESC}`
-  # to the semver components parsed via regex.
-  set-release:
-    runs-on: ubuntu-latest
-    outputs:
-      LEAN_VERSION_MAJOR: ${{ steps.set.outputs.LEAN_VERSION_MAJOR }}
-      LEAN_VERSION_MINOR: ${{ steps.set.outputs.LEAN_VERSION_MINOR }}
-      LEAN_VERSION_PATCH: ${{ steps.set.outputs.LEAN_VERSION_PATCH }}
-      LEAN_SPECIAL_VERSION_DESC: ${{ steps.set.outputs.LEAN_SPECIAL_VERSION_DESC }}
-      RELEASE_TAG: ${{ steps.set.outputs.RELEASE_TAG }}
-    steps:
-      - name: Checkout
-        uses: actions/checkout@v3
-        if: startsWith(github.ref, 'refs/tags/') && github.repository == 'leanprover/lean4'
       - name: Check for official release
         if: startsWith(github.ref, 'refs/tags/') && github.repository == 'leanprover/lean4'
-        id: set
+        id: set-release
         run: |
-          TAG_NAME=${GITHUB_REF##*/}
+          TAG_NAME="${GITHUB_REF##*/}"
 
           # From https://github.com/fsaintjacques/semver-tool/blob/master/src/semver
 
@@ -77,108 +230,29 @@ jobs:
 
           if [[ ${TAG_NAME} =~ ${SEMVER_REGEX} ]]; then
             echo "Tag ${TAG_NAME} matches SemVer regex, with groups ${BASH_REMATCH[1]} ${BASH_REMATCH[2]} ${BASH_REMATCH[3]} ${BASH_REMATCH[4]}"
-            echo "LEAN_VERSION_MAJOR=${BASH_REMATCH[1]}" >> $GITHUB_OUTPUT
-            echo "LEAN_VERSION_MINOR=${BASH_REMATCH[2]}" >> $GITHUB_OUTPUT
-            echo "LEAN_VERSION_PATCH=${BASH_REMATCH[3]}" >> $GITHUB_OUTPUT
-            echo "LEAN_SPECIAL_VERSION_DESC=${BASH_REMATCH[4]##-}" >> $GITHUB_OUTPUT
-            echo "RELEASE_TAG=$TAG_NAME" >> $GITHUB_OUTPUT
+            {
+              echo "LEAN_VERSION_MAJOR=${BASH_REMATCH[1]}"
+              echo "LEAN_VERSION_MINOR=${BASH_REMATCH[2]}"
+              echo "LEAN_VERSION_PATCH=${BASH_REMATCH[3]}"
+              echo "LEAN_SPECIAL_VERSION_DESC=${BASH_REMATCH[4]##-}"
+              echo "RELEASE_TAG=$TAG_NAME"
+            } >> "$GITHUB_OUTPUT"
           else
             echo "Tag ${TAG_NAME} did not match SemVer regex."
           fi
 
   build:
-    needs: [set-nightly, set-release]
+    needs: [configure]
     if: github.event_name != 'schedule' || github.repository == 'leanprover/lean4'
+    strategy:
+      matrix:
+        include: ${{fromJson(needs.configure.outputs.matrix)}}
+      # complete all jobs
+      fail-fast: false
     runs-on: ${{ matrix.os }}
     defaults:
       run:
-        shell: ${{ matrix.shell || 'nix-shell --run "bash -euxo pipefail {0}"' }}
-    strategy:
-      matrix:
-        include:
-          # portable release build: use channel with older glibc (2.27)
-          - name: Linux LLVM
-            os: ubuntu-latest
-            release: false
-            shell: nix-shell --arg pkgsDist "import (fetchTarball \"channel:nixos-19.03\") {{}}" --run "bash -euxo pipefail {0}"
-            llvm-url: https://github.com/leanprover/lean-llvm/releases/download/15.0.1/lean-llvm-x86_64-linux-gnu.tar.zst
-            prepare-llvm: ../script/prepare-llvm-linux.sh lean-llvm*
-            binary-check: ldd -v
-            # foreign code may be linked against more recent glibc
-            # reverse-ffi needs to be updated to link to LLVM libraries
-            CTEST_OPTIONS: -E 'foreign|leanlaketest_reverse-ffi'
-            CMAKE_OPTIONS: -DLLVM=ON -DLLVM_CONFIG=${GITHUB_WORKSPACE}/build/llvm-host/bin/llvm-config
-          - name: Linux release
-            os: ubuntu-latest
-            release: true
-            shell: nix-shell --arg pkgsDist "import (fetchTarball \"channel:nixos-19.03\") {{}}" --run "bash -euxo pipefail {0}"
-            llvm-url: https://github.com/leanprover/lean-llvm/releases/download/15.0.1/lean-llvm-x86_64-linux-gnu.tar.zst
-            prepare-llvm: ../script/prepare-llvm-linux.sh lean-llvm*
-            binary-check: ldd -v
-            # foreign code may be linked against more recent glibc
-            CTEST_OPTIONS: -E 'foreign'
-          - name: Linux
-            os: ubuntu-latest
-            check-stage3: true
-            test-speedcenter: true
-          - name: Linux Debug
-            os: ubuntu-latest
-            CMAKE_OPTIONS: -DCMAKE_BUILD_TYPE=Debug
-            # exclude seriously slow tests
-            CTEST_OPTIONS: -E 'interactivetest|leanpkgtest|laketest|benchtest'
-          - name: Linux fsanitize
-            os: ubuntu-latest
-            # turn off custom allocator & symbolic functions to make LSAN do its magic
-            CMAKE_OPTIONS: -DLEAN_EXTRA_CXX_FLAGS=-fsanitize=address,undefined -DLEANC_EXTRA_FLAGS='-fsanitize=address,undefined -fsanitize-link-c++-runtime' -DSMALL_ALLOCATOR=OFF -DBSYMBOLIC=OFF
-            # exclude seriously slow/problematic tests (laketests crash)
-            CTEST_OPTIONS: -E 'interactivetest|leanpkgtest|laketest|benchtest'
-          - name: macOS
-            os: macos-latest
-            release: true
-            shell: bash -euxo pipefail {0}
-            llvm-url: https://github.com/leanprover/lean-llvm/releases/download/15.0.1/lean-llvm-x86_64-apple-darwin.tar.zst
-            prepare-llvm: ../script/prepare-llvm-macos.sh lean-llvm*
-            binary-check: otool -L
-            tar: gtar  # https://github.com/actions/runner-images/issues/2619
-          - name: macOS aarch64
-            os: macos-latest
-            release: true
-            cross: true
-            shell: bash -euxo pipefail {0}
-            CMAKE_OPTIONS: -DUSE_GMP=OFF -DLEAN_INSTALL_SUFFIX=-darwin_aarch64
-            llvm-url: https://github.com/leanprover/lean-llvm/releases/download/15.0.1/lean-llvm-aarch64-apple-darwin.tar.zst https://github.com/leanprover/lean-llvm/releases/download/15.0.1/lean-llvm-x86_64-apple-darwin.tar.zst
-            prepare-llvm: EXTRA_FLAGS=--target=aarch64-apple-darwin ../script/prepare-llvm-macos.sh lean-llvm-aarch64-* lean-llvm-x86_64-*
-            binary-check: otool -L
-            tar: gtar  # https://github.com/actions/runner-images/issues/2619
-          - name: Windows
-            os: windows-2022
-            release: true
-            shell: msys2 {0}
-            CMAKE_OPTIONS: -G "Unix Makefiles" -DUSE_GMP=OFF
-            # for reasons unknown, interactivetests are flaky on Windows
-            CTEST_OPTIONS: --repeat until-pass:2
-            llvm-url: https://github.com/leanprover/lean-llvm/releases/download/15.0.1/lean-llvm-x86_64-w64-windows-gnu.tar.zst
-            prepare-llvm: ../script/prepare-llvm-mingw.sh lean-llvm*
-            binary-check: ldd
-          - name: Linux aarch64
-            os: ubuntu-latest
-            CMAKE_OPTIONS: -DUSE_GMP=OFF -DLEAN_INSTALL_SUFFIX=-linux_aarch64
-            release: true
-            cross: true
-            shell: nix-shell --arg pkgsDist "import (fetchTarball \"channel:nixos-19.03\") {{ localSystem.config = \"aarch64-unknown-linux-gnu\"; }}" --run "bash -euxo pipefail {0}"
-            llvm-url: https://github.com/leanprover/lean-llvm/releases/download/15.0.1/lean-llvm-x86_64-linux-gnu.tar.zst https://github.com/leanprover/lean-llvm/releases/download/15.0.1/lean-llvm-aarch64-linux-gnu.tar.zst
-            prepare-llvm: EXTRA_FLAGS=--target=aarch64-unknown-linux-gnu ../script/prepare-llvm-linux.sh lean-llvm-aarch64-* lean-llvm-x86_64-*
-          - name: Web Assembly
-            os: ubuntu-latest
-            # Build a native 32bit binary in stage0 and use it to compile the oleans and the wasm build
-            CMAKE_OPTIONS: -DCMAKE_C_COMPILER_WORKS=1 -DSTAGE0_USE_GMP=OFF -DSTAGE0_LEAN_EXTRA_CXX_FLAGS='-m32' -DSTAGE0_LEANC_OPTS='-m32' -DSTAGE0_CMAKE_CXX_COMPILER=clang++ -DSTAGE0_CMAKE_C_COMPILER=clang -DSTAGE0_CMAKE_EXECUTABLE_SUFFIX="" -DUSE_GMP=OFF -DMMAP=OFF -DSTAGE0_MMAP=OFF -DUSE_GMP=OFF -DCMAKE_AR=../emsdk/emsdk-main/upstream/emscripten/emar -DCMAKE_TOOLCHAIN_FILE=../emsdk/emsdk-main/upstream/emscripten/cmake/Modules/Platform/Emscripten.cmake
-            wasm: true
-            cross: true
-            shell: bash -euxo pipefail {0}
-            # Just a few selected test because wasm is slow
-            CTEST_OPTIONS: -R "leantest_1007\.lean|leantest_Format\.lean|leanruntest\_1037.lean|leanruntest_ac_rfl\.lean"
-      # complete all jobs
-      fail-fast: false
+        shell: ${{ matrix.shell || 'nix develop -c bash -euxo pipefail {0}' }}
     name: ${{ matrix.name }}
     env:
       # must be inside workspace
@@ -197,11 +271,13 @@ jobs:
         uses: actions/checkout@v3
         with:
           submodules: true
+          # the default is to use a virtual merge commit between the PR and master: just use the PR
+          ref: ${{ github.event.pull_request.head.sha }}
       - name: Install Nix
         uses: cachix/install-nix-action@v18
         with:
           install_url: https://releases.nixos.org/nix/nix-2.12.0/install
-        if: matrix.os == 'ubuntu-latest' && !matrix.wasm
+        if: matrix.os == 'ubuntu-latest' && !matrix.cmultilib
       - name: Install MSYS2
         uses: msys2/setup-msys2@v2
         with:
@@ -214,7 +290,7 @@ jobs:
           brew install ccache tree zstd coreutils gmp
         if: matrix.os == 'macos-latest'
       - name: Setup emsdk
-        uses: mymindstorm/setup-emsdk@v11
+        uses: mymindstorm/setup-emsdk@v12
         with:
           version: 3.1.44
           actions-cache-folder: emsdk
@@ -223,7 +299,7 @@ jobs:
         run: |
           sudo apt-get update
           sudo apt-get install -y gcc-multilib g++-multilib ccache
-        if: matrix.wasm
+        if: matrix.cmultilib
       - name: Cache
         uses: actions/cache@v3
         with:
@@ -248,21 +324,29 @@ jobs:
           mkdir build
           cd build
           ulimit -c unlimited # coredumps
-          OPTIONS=()
+          # arguments passed to `cmake`
+          # this also enables githash embedding into stage 1 library
+          OPTIONS=(-DCHECK_OLEAN_VERSION=ON)
+          OPTIONS+=(-DLEAN_EXTRA_MAKE_OPTS=-DwarningAsError=true)
+          if [[ -n '${{ matrix.cross_target }}' ]]; then
+            # used by `prepare-llvm`
+            export EXTRA_FLAGS=--target=${{ matrix.cross_target }}
+            OPTIONS+=(-DLEAN_PLATFORM_TARGET=${{ matrix.cross_target }})
+          fi
           if [[ -n '${{ matrix.prepare-llvm }}' ]]; then
             wget -q ${{ matrix.llvm-url }}
             PREPARE="$(${{ matrix.prepare-llvm }})"
             eval "OPTIONS+=($PREPARE)"
           fi
-          if [[ -n '${{ matrix.release }}' && -n '${{ needs.set-nightly.outputs.nightly }}' ]]; then
-            OPTIONS+=(-DLEAN_SPECIAL_VERSION_DESC=${{ needs.set-nightly.outputs.nightly }})
+          if [[ -n '${{ matrix.release }}' && -n '${{ needs.configure.outputs.nightly }}' ]]; then
+            OPTIONS+=(-DLEAN_SPECIAL_VERSION_DESC=${{ needs.configure.outputs.nightly }})
           fi
-          if [[ -n '${{ matrix.release }}' && -n '${{ needs.set-release.outputs.RELEASE_TAG }}' ]]; then
-            OPTIONS+=(-DLEAN_VERSION_MAJOR=${{ needs.set-release.outputs.LEAN_VERSION_MAJOR }})
-            OPTIONS+=(-DLEAN_VERSION_MINOR=${{ needs.set-release.outputs.LEAN_VERSION_MINOR }})
-            OPTIONS+=(-DLEAN_VERSION_PATCH=${{ needs.set-release.outputs.LEAN_VERSION_PATCH }})
+          if [[ -n '${{ matrix.release }}' && -n '${{ needs.configure.outputs.RELEASE_TAG }}' ]]; then
+            OPTIONS+=(-DLEAN_VERSION_MAJOR=${{ needs.configure.outputs.LEAN_VERSION_MAJOR }})
+            OPTIONS+=(-DLEAN_VERSION_MINOR=${{ needs.configure.outputs.LEAN_VERSION_MINOR }})
+            OPTIONS+=(-DLEAN_VERSION_PATCH=${{ needs.configure.outputs.LEAN_VERSION_PATCH }})
             OPTIONS+=(-DLEAN_VERSION_IS_RELEASE=1)
-            OPTIONS+=(-DLEAN_SPECIAL_VERSION_DESC=${{ needs.set-release.outputs.LEAN_SPECIAL_VERSION_DESC }})
+            OPTIONS+=(-DLEAN_SPECIAL_VERSION_DESC=${{ needs.configure.outputs.LEAN_SPECIAL_VERSION_DESC }})
           fi
           # contortion to support empty OPTIONS with old macOS bash
           cmake .. ${{ matrix.CMAKE_OPTIONS }} ${OPTIONS[@]+"${OPTIONS[@]}"} -DLEAN_INSTALL_PREFIX=$PWD/..
@@ -273,13 +357,13 @@ jobs:
       - name: List Install Tree
         run: |
           # omit contents of Init/, ...
-          tree --du -h lean-* | grep -E ' (Init|Lean|Lake|LICENSE|[a-z])'
+          tree --du -h lean-*-* | grep -E ' (Init|Lean|Lake|LICENSE|[a-z])'
       - name: Pack
         run: |
-          dir=$(echo lean-*)
+          dir=$(echo lean-*-*)
           mkdir pack
           # high-compression tar.zst + zip for release, fast tar.zst otherwise
-          if [[ '${{ startsWith(github.ref, 'refs/tags/') && matrix.release }}' == true || -n '${{ needs.set-nightly.outputs.nightly }}' || -n '${{ needs.set-release.outputs.RELEASE_TAG }}' ]]; then
+          if [[ '${{ startsWith(github.ref, 'refs/tags/') && matrix.release }}' == true || -n '${{ needs.configure.outputs.nightly }}' || -n '${{ needs.configure.outputs.RELEASE_TAG }}' ]]; then
             ${{ matrix.tar || 'tar' }} cf - $dir | zstd -T0 --no-progress -19 -o pack/$dir.tar.zst
             zip -rq pack/$dir.zip $dir
           else
@@ -300,22 +384,22 @@ jobs:
           ulimit -c unlimited # coredumps
           # exclude nonreproducible test
           ctest -j4 --output-on-failure ${{ matrix.CTEST_OPTIONS }} < /dev/null
-        if: matrix.wasm || !matrix.cross
+        if: (matrix.wasm || !matrix.cross) && needs.configure.outputs.quick == 'false'
       - name: Check Test Binary
         run: ${{ matrix.binary-check }} tests/compiler/534.lean.out
-        if: ${{ !matrix.cross }}
+        if: ${{ !matrix.cross && needs.configure.outputs.quick == 'false' }}
       - name: Build Stage 2
         run: |
           cd build
           ulimit -c unlimited # coredumps
           make -j4 stage2
-        if: matrix.build-stage2 || matrix.check-stage3
+        if: matrix.test-speedcenter
       - name: Check Stage 3
         run: |
           cd build
           ulimit -c unlimited # coredumps
           make -j4 check-stage3
-        if: matrix.check-stage3
+        if: matrix.test-speedcenter
       - name: Test Speedcenter Benchmarks
         run: |
           echo -1 | sudo tee /proc/sys/kernel/perf_event_paranoid
@@ -327,30 +411,49 @@ jobs:
         run: |
           cd build
           ulimit -c unlimited # coredumps
-          make update-stage0 && make -j4
-        if: matrix.name == 'Linux'
+          # clean rebuild in case of Makefile changes
+          make update-stage0 && rm -rf ./stage* && make -j4
+        if: matrix.name == 'Linux' && needs.configure.outputs.quick == 'false'
       - name: CCache stats
         run: ccache -s
       - name: Show stacktrace for coredumps
-        if: ${{ failure() }} && matrix.os == 'ubuntu-latest'
+        if: ${{ failure() && matrix.os == 'ubuntu-latest' }}
         run: |
           for c in coredumps/*; do
             progbin="$(file $c | sed "s/.*execfn: '\([^']*\)'.*/\1/")"
             echo bt | $GDB/bin/gdb -q $progbin $c || true
           done
-      - name: Upload coredumps
-        uses: actions/upload-artifact@v3
-        if: ${{ failure() }} && matrix.os == 'ubuntu-latest'
-        with:
-          name: coredumps-${{ matrix.name }}
-          path: |
-            ./coredumps
-            ./build/stage0/bin/lean
-            ./build/stage0/lib/lean/libleanshared.so
-            ./build/stage1/bin/lean
-            ./build/stage1/lib/lean/libleanshared.so
-            ./build/stage2/bin/lean
-            ./build/stage2/lib/lean/libleanshared.so
+      # has not been used in a long while, would need to be adapted to new
+      # shared libs
+      #- name: Upload coredumps
+      #  uses: actions/upload-artifact@v3
+      #  if: ${{ failure() && matrix.os == 'ubuntu-latest' }}
+      #  with:
+      #    name: coredumps-${{ matrix.name }}
+      #    path: |
+      #      ./coredumps
+      #      ./build/stage0/bin/lean
+      #      ./build/stage0/lib/lean/libleanshared.so
+      #      ./build/stage1/bin/lean
+      #      ./build/stage1/lib/lean/libleanshared.so
+      #      ./build/stage2/bin/lean
+      #      ./build/stage2/lib/lean/libleanshared.so
+
+  # This job collects results from all the matrix jobs
+  # This can be made the “required” job, instead of listing each
+  # matrix job separately
+  all-done:
+    name: Build matrix complete
+    runs-on: ubuntu-latest
+    needs: build
+    # mark as merely cancelled not failed if builds are cancelled
+    if: ${{ !cancelled() }}
+    steps:
+    - if: contains(needs.*.result, 'failure')
+      uses: actions/github-script@v7
+      with:
+        script: |
+            core.setFailed('Some jobs failed')
 
   # This job creates releases from tags
   # (whether they are "unofficial" releases for experiments, or official releases when the tag is "v" followed by a semver string.)
@@ -375,8 +478,8 @@ jobs:
   # This job creates nightly releases during the cron job.
   # It is responsible for creating the tag, and automatically generating a changelog.
   release-nightly:
-    needs: [set-nightly, build]
-    if: needs.set-nightly.outputs.nightly
+    needs: [configure, build]
+    if: needs.configure.outputs.nightly
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
@@ -392,15 +495,16 @@ jobs:
         run: |
           git remote add nightly https://foo:'${{ secrets.PUSH_NIGHTLY_TOKEN }}'@github.com/${{ github.repository_owner }}/lean4-nightly.git
           git fetch nightly --tags
-          git tag ${{ needs.set-nightly.outputs.nightly }}
-          git push nightly ${{ needs.set-nightly.outputs.nightly }}
-          last_tag=$(git log HEAD^ --simplify-by-decoration --pretty="format:%d" | grep -o "nightly-[-0-9]*" | head -n 1)
+          git tag "${{ needs.configure.outputs.nightly }}"
+          git push nightly "${{ needs.configure.outputs.nightly }}"
+          git push -f origin refs/tags/${{ needs.configure.outputs.nightly }}:refs/heads/nightly
+          last_tag="$(git log HEAD^ --simplify-by-decoration --pretty="format:%d" | grep -o "nightly-[-0-9]*" | head -n 1)"
           echo -e "*Changes since ${last_tag}:*\n\n" > diff.md
-          git show $last_tag:RELEASES.md > old.md
+          git show "$last_tag":RELEASES.md > old.md
           #./script/diff_changelogs.py old.md doc/changes.md >> diff.md
           diff --changed-group-format='%>' --unchanged-group-format='' old.md RELEASES.md >> diff.md || true
           echo -e "\n*Full commit log*\n" >> diff.md
-          git log --oneline $last_tag..HEAD | sed 's/^/* /' >> diff.md
+          git log --oneline "$last_tag"..HEAD | sed 's/^/* /' >> diff.md
       - name: Release Nightly
         uses: softprops/action-gh-release@v1
         with:
@@ -408,7 +512,7 @@ jobs:
           prerelease: true
           files: artifacts/*/*
           fail_on_unmatched_files: true
-          tag_name: ${{ needs.set-nightly.outputs.nightly }}
+          tag_name: ${{ needs.configure.outputs.nightly }}
           repository: ${{ github.repository_owner }}/lean4-nightly
         env:
           GITHUB_TOKEN: ${{ secrets.PUSH_NIGHTLY_TOKEN }}

.github/workflows/copyright-header.yml

@@ -0,0 +1,20 @@
+name: Check for copyright header
+
+on: [pull_request]
+
+jobs:
+  check-lean-files:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+
+    - name: Verify .lean files start with a copyright header.
+      run: |
+        FILES=$(find . -type d \( -path "./tests" -o -path "./doc" -o -path "./src/lake/examples" -o -path "./src/lake/tests" -o -path "./build" -o -path "./nix" \) -prune -o -type f -name "*.lean" -exec perl -ne 'BEGIN { $/ = undef; } print "$ARGV\n" if !m{\A/-\nCopyright}; exit;' {} \;)
+        if [ -n "$FILES" ]; then
+          echo "Found .lean files which do not have a copyright header:"
+          echo "$FILES"
+          exit 1
+        else
+          echo "All copyright headers present."
+        fi

.github/workflows/labels-from-comments.yml

@@ -15,7 +15,7 @@ jobs:
 
     steps:
     - name: Add label based on comment
-      uses: actions/github-script@v6
+      uses: actions/github-script@v7
       with:
         github-token: ${{ secrets.GITHUB_TOKEN }}
         script: |

.github/workflows/nix-ci.yml

@@ -6,8 +6,8 @@ on:
     tags:
       - '*'
   pull_request:
-    branches:
-      - master
+    types: [opened, synchronize, reopened, labeled]
+  merge_group:
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
@@ -18,7 +18,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     defaults:
       run:
-        shell: nix -v --experimental-features "nix-command flakes" run .#ciShell -- bash -euxo pipefail {0}
+        shell: nix run .#ciShell -- bash -euxo pipefail {0}
     strategy:
       matrix:
         include:
@@ -30,18 +30,13 @@ jobs:
       fail-fast: false
     name: ${{ matrix.name }}
     env:
-      NIX_BUILD_ARGS: -v --print-build-logs --fallback
+      NIX_BUILD_ARGS: --print-build-logs --fallback
     steps:
       - name: Checkout
         uses: actions/checkout@v3
-      - name: Install Nix
-        uses: cachix/install-nix-action@v18
         with:
-          # https://github.com/NixOS/nix/issues/6572
-          install_url: https://releases.nixos.org/nix/nix-2.7.0/install
-          extra_nix_config: |
-            extra-sandbox-paths = /nix/var/cache/ccache
-            substituters = file://${{ github.workspace }}/nix-store-cache-copy?priority=10&trusted=true https://cache.nixos.org
+          # the default is to use a virtual merge commit between the PR and master: just use the PR
+          ref: ${{ github.event.pull_request.head.sha }}
       - name: Set Up Nix Cache
         uses: actions/cache@v3
         with:
@@ -55,8 +50,13 @@ jobs:
         run: |
           # Nix seems to mutate the cache, so make a copy
           cp -r nix-store-cache nix-store-cache-copy || true
+      - name: Install Nix
+        uses: DeterminateSystems/nix-installer-action@main
+        with:
+          extra-conf: |
+            extra-sandbox-paths = /nix/var/cache/ccache?
+            substituters = file://${{ github.workspace }}/nix-store-cache-copy?priority=10&trusted=true https://cache.nixos.org  
       - name: Prepare CCache Cache
-        shell: bash -euxo pipefail {0}
         run: |
           sudo mkdir -m0770 -p /nix/var/cache/ccache
           sudo chown -R $USER /nix/var/cache/ccache
@@ -69,16 +69,9 @@ jobs:
           restore-keys: |
             ${{ matrix.name }}-nix-ccache
       - name: Further Set Up CCache Cache
-        shell: bash -euxo pipefail {0}
         run: |
           sudo chown -R root:nixbld /nix/var/cache
           sudo chmod -R 770 /nix/var/cache
-      - name: Install Cachix
-        uses: cachix/cachix-action@v12
-        with:
-          name: lean4
-          authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
-          skipPush: true  # we push specific outputs only
       - name: Build
         run: |
           nix build $NIX_BUILD_ARGS .#cacheRoots -o push-build
@@ -89,21 +82,44 @@ jobs:
         run: |
           nix build $NIX_BUILD_ARGS --update-input lean --no-write-lock-file ./doc#{lean-mdbook,leanInk,alectryon,test,inked} -o push-doc
           nix build $NIX_BUILD_ARGS --update-input lean --no-write-lock-file ./doc
+          # https://github.com/netlify/cli/issues/1809
+          cp -r --dereference ./result ./dist
         if: matrix.name == 'Nix Linux'
-      - name: Push to Cachix
-        run: |
-          [ -z "${{ secrets.CACHIX_AUTH_TOKEN }}" ] || cachix push -j4 lean4 ./push-* || true
+      - name: Check manual for broken links
+        id: lychee
+        uses: lycheeverse/lychee-action@v1.9.0
+        with:
+          fail: false  # report errors but do not block CI on temporary failures
+          # gmplib.org consistently times out from GH actions
+          # the GitHub token is to avoid rate limiting
+          args: --base './dist' --no-progress --github-token ${{ secrets.GITHUB_TOKEN }} --exclude 'gmplib.org' './dist/**/*.html'
       - name: Rebuild Nix Store Cache
         run: |
           rm -rf nix-store-cache || true
           nix copy ./push-* --to file://$PWD/nix-store-cache?compression=none
-      - name: Publish manual
-        uses: peaceiris/actions-gh-pages@v3
+      - id: deploy-info
+        name: Compute Deployment Metadata
+        run: |
+          set -e
+          python3 -c 'import base64; print("alias="+base64.urlsafe_b64encode(bytes.fromhex("${{github.sha}}")).decode("utf-8").rstrip("="))' >> "$GITHUB_OUTPUT"
+          echo "message=`git log -1 --pretty=format:"%s"`" >> "$GITHUB_OUTPUT"
+      - name: Publish manual to Netlify
+        uses: nwtgck/actions-netlify@v2.0
+        id: publish-manual
         with:
-          github_token: ${{ secrets.GITHUB_TOKEN }}
-          publish_dir: ./result
-          destination_dir: ./doc
-        if: matrix.name == 'Nix Linux' && github.ref == 'refs/heads/master' && github.event_name == 'push'
+          publish-dir: ./dist
+          production-branch: master
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          deploy-message: |
+            ${{ github.event_name == 'pull_request' && format('pr#{0}: {1}', github.event.number, github.event.pull_request.title) || format('ref/{0}: {1}', github.ref_name, steps.deploy-info.outputs.message) }}
+          alias: ${{ steps.deploy-info.outputs.alias }}
+          enable-commit-comment: false
+          enable-pull-request-comment: false
+          github-deployment-environment: "lean-lang.org/lean4/doc"
+          fails-without-credentials: false
+        env:
+          NETLIFY_AUTH_TOKEN: ${{ secrets.NETLIFY_AUTH_TOKEN }}
+          NETLIFY_SITE_ID: "b8e805d2-7e9b-4f80-91fb-a84d72fc4a68"
       - name: Fixup CCache Cache
         run: |
           sudo chown -R $USER /nix/var/cache

.github/workflows/pr-release.yml

@@ -6,6 +6,10 @@
 # Instead we use `workflow_run`, which essentially allows us to escalate privileges
 # (but only runs the CI as described in the `master` branch, not in the PR branch).
 
+# The main specification/documentation for this workflow is at
+# https://leanprover-community.github.io/contribute/tags_and_branches.html
+# Keep that in sync!
+
 name: PR release
 
 on:
@@ -16,25 +20,16 @@ on:
 jobs:
   on-success:
     runs-on: ubuntu-latest
-    if: github.event.workflow_run.conclusion == 'success' && github.repository == 'leanprover/lean4'
+    if: github.event.workflow_run.conclusion == 'success' && github.event.workflow_run.event == 'pull_request' && github.repository == 'leanprover/lean4'
     steps:
       - name: Retrieve information about the original workflow
         uses: potiuk/get-workflow-origin@v1_1 # https://github.com/marketplace/actions/get-workflow-origin
+        # This action is deprecated and archived, but it seems hard to find a better solution for getting the PR number
+        # see https://github.com/orgs/community/discussions/25220 for some discussion
         id: workflow-info
         with:
           token: ${{ secrets.GITHUB_TOKEN }}
           sourceRunId: ${{ github.event.workflow_run.id }}
-      - name: Checkout
-        # Only proceed if the previous workflow had a pull request number.
-        if: ${{ steps.workflow-info.outputs.pullRequestNumber != '' }}
-        uses: actions/checkout@v3
-        with:
-          token: ${{ secrets.PR_RELEASES_TOKEN }}
-          # Since `workflow_run` runs on master, we need to specify which commit to check out,
-          # so that we tag the PR.
-          ref: ${{ steps.workflow-info.outputs.targetCommitSha }}
-          # We need a full checkout, so that we can push the PR commits to the `lean4-pr-releases` repo.
-          fetch-depth: 0
 
       - name: Download artifact from the previous workflow.
         if: ${{ steps.workflow-info.outputs.pullRequestNumber != '' }}
@@ -45,14 +40,22 @@ jobs:
           path: artifacts
           name: build-.*
           name_is_regexp: true
-      - name: Prepare release
+
+      - name: Push tag
+        if: ${{ steps.workflow-info.outputs.pullRequestNumber != '' }}
+        run: |
+          git init --bare lean4.git
+          git -C lean4.git remote add origin https://github.com/${{ github.repository_owner }}/lean4.git
+          git -C lean4.git fetch -n origin master
+          git -C lean4.git fetch -n origin "${{ steps.workflow-info.outputs.sourceHeadSha }}"
+          git -C lean4.git tag -f pr-release-${{ steps.workflow-info.outputs.pullRequestNumber }} "${{ steps.workflow-info.outputs.sourceHeadSha }}"
+          git -C lean4.git remote add pr-releases https://foo:'${{ secrets.PR_RELEASES_TOKEN }}'@github.com/${{ github.repository_owner }}/lean4-pr-releases.git
+          git -C lean4.git push -f pr-releases pr-release-${{ steps.workflow-info.outputs.pullRequestNumber }}
+      - name: Delete existing release if present
         if: ${{ steps.workflow-info.outputs.pullRequestNumber != '' }}
         run: |
-          git remote add pr-releases https://foo:'${{ secrets.PR_RELEASES_TOKEN }}'@github.com/${{ github.repository_owner }}/lean4-pr-releases.git
           # Try to delete any existing release for the current PR.
           gh release delete --repo ${{ github.repository_owner }}/lean4-pr-releases pr-release-${{ steps.workflow-info.outputs.pullRequestNumber }} -y || true
-          git tag -f pr-release-${{ steps.workflow-info.outputs.pullRequestNumber }}
-          git push -f pr-releases pr-release-${{ steps.workflow-info.outputs.pullRequestNumber }}
         env:
           GH_TOKEN: ${{ secrets.PR_RELEASES_TOKEN }}
       - name: Release
@@ -70,57 +73,265 @@ jobs:
           # The token used here must have `workflow` privileges.
           GITHUB_TOKEN: ${{ secrets.PR_RELEASES_TOKEN }}
 
+      - name: Report release status
+        if: ${{ steps.workflow-info.outputs.pullRequestNumber != '' }}
+        uses: actions/github-script@v6
+        with:
+          script: |
+            await github.rest.repos.createCommitStatus({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              sha: "${{ steps.workflow-info.outputs.sourceHeadSha }}",
+              state: "success",
+              context: "PR toolchain",
+              description: "${{ github.repository_owner }}/lean4-pr-releases:pr-release-${{ steps.workflow-info.outputs.pullRequestNumber }}",
+            });
+
       - name: Add label
         if: ${{ steps.workflow-info.outputs.pullRequestNumber != '' }}
-        uses: actions-ecosystem/action-add-labels@v1
+        uses: actions/github-script@v7
         with:
-          number: ${{ steps.workflow-info.outputs.pullRequestNumber }}
-          labels: toolchain-available
+          script: |
+            await github.rest.issues.addLabels({
+              issue_number: ${{ steps.workflow-info.outputs.pullRequestNumber }},
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              labels: ['toolchain-available']
+            })
 
-      # We next automatically create a Mathlib branch using this toolchain.
-      # Mathlib CI will be responsible for reporting back success or failure
-      # to the PR comments asynchronously.
-      - name: Cleanup workspace
+      # Next, determine the most recent nightly release in this PR's history.
+      - name: Find most recent nightly in feature branch
+        id: most-recent-nightly-tag
         if: ${{ steps.workflow-info.outputs.pullRequestNumber != '' }}
         run: |
-          sudo rm -rf *
+          git -C lean4.git remote add nightly https://github.com/leanprover/lean4-nightly.git
+          git -C lean4.git fetch nightly '+refs/tags/nightly-*:refs/tags/nightly-*'
+          git -C lean4.git tag --merged "${{ steps.workflow-info.outputs.sourceHeadSha }}" --list "nightly-*" \
+            | sort -rV | head -n 1 | sed "s/^nightly-*/MOST_RECENT_NIGHTLY=/" | tee -a "$GITHUB_ENV"
 
-      # Checkout the mathlib4 repository with all branches
-      - name: Checkout mathlib4 repository
-        uses: actions/checkout@v2
-        with:
-          repository: leanprover-community/mathlib4
-          token: ${{ secrets.MATHLIB4_BOT }}
-          ref: nightly-testing # This is more likely than `master` to work with the base of this PR.
-          fetch-depth: 0
-
-      - name: Check if branch exists
+      - name: 'Setup jq'
         if: ${{ steps.workflow-info.outputs.pullRequestNumber != '' }}
-        id: check_branch
+        uses: dcarbone/install-jq-action@v1.0.1
+
+      # Check that the most recently nightly coincides with 'git merge-base HEAD master'
+      - name: Check merge-base and nightly-testing-YYYY-MM-DD
+        if: ${{ steps.workflow-info.outputs.pullRequestNumber != '' }}
+        id: ready
+        run: |
+          echo "Most recent nightly release in your branch: $MOST_RECENT_NIGHTLY"
+          NIGHTLY_SHA=$(git -C lean4.git rev-parse "nightly-$MOST_RECENT_NIGHTLY^{commit}")
+          echo "SHA of most recent nightly release: $NIGHTLY_SHA"
+          MERGE_BASE_SHA=$(git -C lean4.git merge-base origin/master "${{ steps.workflow-info.outputs.sourceHeadSha }}")
+          echo "SHA of merge-base: $MERGE_BASE_SHA"
+          if [ "$NIGHTLY_SHA" = "$MERGE_BASE_SHA" ]; then
+            echo "The merge base of this PR coincides with the nightly release"
+
+            STD_REMOTE_TAGS="$(git ls-remote https://github.com/leanprover/std4.git nightly-testing-"$MOST_RECENT_NIGHTLY")"
+            MATHLIB_REMOTE_TAGS="$(git ls-remote https://github.com/leanprover-community/mathlib4.git nightly-testing-"$MOST_RECENT_NIGHTLY")"
+
+            if [[ -n "$STD_REMOTE_TAGS" ]]; then
+              echo "... and Std has a 'nightly-testing-$MOST_RECENT_NIGHTLY' tag."
+              MESSAGE=""
+
+              if [[ -n "$MATHLIB_REMOTE_TAGS" ]]; then
+                echo "... and Mathlib has a 'nightly-testing-$MOST_RECENT_NIGHTLY' tag."    
+              else
+                echo "... but Mathlib does not yet have a 'nightly-testing-$MOST_RECENT_NIGHTLY' tag."
+                MESSAGE="- ❗ Mathlib CI can not be attempted yet, as the \`nightly-testing-$MOST_RECENT_NIGHTLY\` tag does not exist there yet. We will retry when you push more commits. If you rebase your branch onto \`nightly-with-mathlib\`, Mathlib CI should run now."
+              fi
+            else
+              echo "... but Std does not yet have a 'nightly-testing-$MOST_RECENT_NIGHTLY' tag."
+              MESSAGE="- ❗ Std CI can not be attempted yet, as the \`nightly-testing-$MOST_RECENT_NIGHTLY\` tag does not exist there yet. We will retry when you push more commits. If you rebase your branch onto \`nightly-with-mathlib\`, Std CI should run now."
+            fi
+
+          else
+            echo "The most recently nightly tag on this branch has SHA: $NIGHTLY_SHA"
+            echo "but 'git merge-base origin/master HEAD' reported: $MERGE_BASE_SHA"
+            git -C lean4.git log -10 origin/master
+
+            MESSAGE="- ❗ Std/Mathlib CI will not be attempted unless your PR branches off the \`nightly-with-mathlib\` branch. Try \`git rebase $MERGE_BASE_SHA --onto $NIGHTLY_SHA\`."
+          fi
+
+          if [[ -n "$MESSAGE" ]]; then
+
+            echo "Checking existing messages"
+
+            # The code for updating comments is duplicated in mathlib's
+            # scripts/lean-pr-testing-comments.sh
+            # so keep in sync
+
+            # Use GitHub API to check if a comment already exists
+            existing_comment="$(curl -L -s -H "Authorization: token ${{ secrets.MATHLIB4_BOT }}" \
+                                    -H "Accept: application/vnd.github.v3+json" \
+                                    "https://api.github.com/repos/leanprover/lean4/issues/${{ steps.workflow-info.outputs.pullRequestNumber }}/comments" \
+                                    | jq 'first(.[] | select(.body | test("^- . Mathlib") or startswith("Mathlib CI status")) | select(.user.login == "leanprover-community-mathlib4-bot"))')"
+            existing_comment_id="$(echo "$existing_comment" | jq -r .id)"
+            existing_comment_body="$(echo "$existing_comment" | jq -r .body)"
+
+            if [[ "$existing_comment_body" != *"$MESSAGE"* ]]; then
+              MESSAGE="$MESSAGE ($(date "+%Y-%m-%d %H:%M:%S"))"
+
+              echo "Posting message to the comments: $MESSAGE"
+
+              # Append new result to the existing comment or post a new comment
+              # It's essential we use the MATHLIB4_BOT token here, so that Mathlib CI can subsequently edit the comment.
+              if [ -z "$existing_comment_id" ]; then
+                INTRO="Mathlib CI status ([docs](https://leanprover-community.github.io/contribute/tags_and_branches.html)):"
+                # Post new comment with a bullet point
+                echo "Posting as new comment at leanprover/lean4/issues/${{ steps.workflow-info.outputs.pullRequestNumber }}/comments"
+                curl -L -s \
+                  -X POST \
+                  -H "Authorization: token ${{ secrets.MATHLIB4_BOT }}" \
+                  -H "Accept: application/vnd.github.v3+json" \
+                  -d "$(jq --null-input --arg intro "$INTRO" --arg val "$MESSAGE" '{"body":($intro + "\n" + $val)}')" \
+                  "https://api.github.com/repos/leanprover/lean4/issues/${{ steps.workflow-info.outputs.pullRequestNumber }}/comments"
+              else
+                # Append new result to the existing comment
+                echo "Appending to existing comment at leanprover/lean4/issues/${{ steps.workflow-info.outputs.pullRequestNumber }}/comments"
+                curl -L -s \
+                  -X PATCH \
+                  -H "Authorization: token ${{ secrets.MATHLIB4_BOT }}" \
+                  -H "Accept: application/vnd.github.v3+json" \
+                  -d "$(jq --null-input --arg existing "$existing_comment_body" --arg message "$MESSAGE" '{"body":($existing + "\n" + $message)}')" \
+                  "https://api.github.com/repos/leanprover/lean4/issues/comments/$existing_comment_id"
+              fi
+            else
+              echo "The message already exists in the comment body."
+            fi
+            echo "mathlib_ready=false" >> "$GITHUB_OUTPUT"
+          else
+            echo "mathlib_ready=true" >> "$GITHUB_OUTPUT"
+          fi
+
+      - name: Report mathlib base
+        if: ${{ steps.workflow-info.outputs.pullRequestNumber != '' && steps.ready.outputs.mathlib_ready == 'true' }}
+        uses: actions/github-script@v6
+        with:
+          script: |
+            const description =
+              process.env.MOST_RECENT_NIGHTLY ?
+              "nightly-" + process.env.MOST_RECENT_NIGHTLY :
+              "not branched off nightly";
+            await github.rest.repos.createCommitStatus({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              sha: "${{ steps.workflow-info.outputs.sourceHeadSha }}",
+              state: "success",
+              context: "PR branched off:",
+              description: description,
+            });
+
+      # We next automatically create a Std branch using this toolchain.
+      # Std doesn't itself have a mechanism to report results of CI from this branch back to Lean
+      # Instead this is taken care of by Mathlib CI, which will fail if Std fails.
+      - name: Cleanup workspace
+        if: steps.workflow-info.outputs.pullRequestNumber != '' && steps.ready.outputs.mathlib_ready == 'true'
+        run: |
+          sudo rm -rf ./*
+
+      # Checkout the Std repository with all branches
+      - name: Checkout Std repository
+        if: steps.workflow-info.outputs.pullRequestNumber != '' && steps.ready.outputs.mathlib_ready == 'true'
+        uses: actions/checkout@v3
+        with:
+          repository: leanprover/std4
+          token: ${{ secrets.MATHLIB4_BOT }}
+          ref: nightly-testing
+          fetch-depth: 0 # This ensures we check out all tags and branches.
+
+      - name: Check if tag exists
+        if: steps.workflow-info.outputs.pullRequestNumber != '' && steps.ready.outputs.mathlib_ready == 'true'
+        id: check_std_tag
         run: |
           git config user.name "leanprover-community-mathlib4-bot"
           git config user.email "leanprover-community-mathlib4-bot@users.noreply.github.com"
 
-          EXISTS=$(git ls-remote --heads origin lean-pr-testing-${{ steps.workflow-info.outputs.pullRequestNumber }} | wc -l)
+          if git ls-remote --heads --tags --exit-code origin "nightly-testing-${MOST_RECENT_NIGHTLY}" >/dev/null; then
+            BASE="nightly-testing-${MOST_RECENT_NIGHTLY}"
+          else
+            echo "This shouldn't be possible: couldn't find a 'nightly-testing-${MOST_RECENT_NIGHTLY}' tag at Std. Falling back to 'nightly-testing'."
+            BASE=nightly-testing
+          fi
+
+          echo "Using base branch: $BASE"
+
+          EXISTS="$(git ls-remote --heads origin lean-pr-testing-${{ steps.workflow-info.outputs.pullRequestNumber }} | wc -l)"
           echo "Branch exists: $EXISTS"
           if [ "$EXISTS" = "0" ]; then
             echo "Branch does not exist, creating it."
-            git checkout -b lean-pr-testing-${{ steps.workflow-info.outputs.pullRequestNumber }}
+            git switch -c lean-pr-testing-${{ steps.workflow-info.outputs.pullRequestNumber }} "$BASE"
             echo "leanprover/lean4-pr-releases:pr-release-${{ steps.workflow-info.outputs.pullRequestNumber }}" > lean-toolchain
             git add lean-toolchain
             git commit -m "Update lean-toolchain for testing https://github.com/leanprover/lean4/pull/${{ steps.workflow-info.outputs.pullRequestNumber }}"
           else
             echo "Branch already exists, pushing an empty commit."
-            git checkout lean-pr-testing-${{ steps.workflow-info.outputs.pullRequestNumber }}
-            # The Mathlib `nightly-testing` branch may have moved since this branch was created, so merge their changes.
-            # If the base of this Lean4 PR becomes significantly older than the nightly being used by `nightly-testing`
-            # this will cause breakages rather than fixing them!
-            # Without cumbersome requirements that Lean4 PRs are based off nightlies, I'm not sure there is a perfect solution here.
-            git merge nightly-testing --strategy-option ours --no-commit --allow-unrelated-histories
+            git switch lean-pr-testing-${{ steps.workflow-info.outputs.pullRequestNumber }}
+            # The Std `nightly-testing` or `nightly-testing-YYYY-MM-DD` branch may have moved since this branch was created, so merge their changes.
+            # (This should no longer be possible once `nightly-testing-YYYY-MM-DD` is a tag, but it is still safe to merge.)
+            git merge "$BASE" --strategy-option ours --no-commit --allow-unrelated-histories
             git commit --allow-empty -m "Trigger CI for https://github.com/leanprover/lean4/pull/${{ steps.workflow-info.outputs.pullRequestNumber }}"
           fi
 
       - name: Push changes
-        if: ${{ steps.workflow-info.outputs.pullRequestNumber != '' }}
+        if: steps.workflow-info.outputs.pullRequestNumber != '' && steps.ready.outputs.mathlib_ready == 'true'
+        run: |
+          git push origin lean-pr-testing-${{ steps.workflow-info.outputs.pullRequestNumber }}
+
+
+      # We next automatically create a Mathlib branch using this toolchain.
+      # Mathlib CI will be responsible for reporting back success or failure
+      # to the PR comments asynchronously.
+      - name: Cleanup workspace
+        if: steps.workflow-info.outputs.pullRequestNumber != '' && steps.ready.outputs.mathlib_ready == 'true'
+        run: |
+          sudo rm -rf ./*
+
+      # Checkout the mathlib4 repository with all branches
+      - name: Checkout mathlib4 repository
+        if: steps.workflow-info.outputs.pullRequestNumber != '' && steps.ready.outputs.mathlib_ready == 'true'
+        uses: actions/checkout@v3
+        with:
+          repository: leanprover-community/mathlib4
+          token: ${{ secrets.MATHLIB4_BOT }}
+          ref: nightly-testing
+          fetch-depth: 0 # This ensures we check out all tags and branches.
+
+      - name: Check if tag exists
+        if: steps.workflow-info.outputs.pullRequestNumber != '' && steps.ready.outputs.mathlib_ready == 'true'
+        id: check_mathlib_tag
+        run: |
+          git config user.name "leanprover-community-mathlib4-bot"
+          git config user.email "leanprover-community-mathlib4-bot@users.noreply.github.com"
+
+          if git ls-remote --heads --tags --exit-code origin "nightly-testing-${MOST_RECENT_NIGHTLY}" >/dev/null; then
+            BASE="nightly-testing-${MOST_RECENT_NIGHTLY}"
+          else
+            echo "This shouldn't be possible: couldn't find a 'nightly-testing-${MOST_RECENT_NIGHTLY}' branch at Mathlib. Falling back to 'nightly-testing'."
+            BASE=nightly-testing
+          fi
+
+          echo "Using base tag: $BASE"
+
+          EXISTS="$(git ls-remote --heads origin lean-pr-testing-${{ steps.workflow-info.outputs.pullRequestNumber }} | wc -l)"
+          echo "Branch exists: $EXISTS"
+          if [ "$EXISTS" = "0" ]; then
+            echo "Branch does not exist, creating it."
+            git switch -c lean-pr-testing-${{ steps.workflow-info.outputs.pullRequestNumber }} "$BASE"
+            echo "leanprover/lean4-pr-releases:pr-release-${{ steps.workflow-info.outputs.pullRequestNumber }}" > lean-toolchain
+            git add lean-toolchain
+            sed -i "s/require std from git \"https:\/\/github.com\/leanprover\/std4\" @ \".\+\"/require std from git \"https:\/\/github.com\/leanprover\/std4\" @ \"nightly-testing-${MOST_RECENT_NIGHTLY}\"/" lakefile.lean
+            git add lakefile.lean
+            git commit -m "Update lean-toolchain for testing https://github.com/leanprover/lean4/pull/${{ steps.workflow-info.outputs.pullRequestNumber }}"
+          else
+            echo "Branch already exists, pushing an empty commit."
+            git switch lean-pr-testing-${{ steps.workflow-info.outputs.pullRequestNumber }}
+            # The Mathlib `nightly-testing` branch or `nightly-testing-YYYY-MM-DD` tag may have moved since this branch was created, so merge their changes.
+            # (This should no longer be possible once `nightly-testing-YYYY-MM-DD` is a tag, but it is still safe to merge.)
+            git merge "$BASE" --strategy-option ours --no-commit --allow-unrelated-histories
+            git commit --allow-empty -m "Trigger CI for https://github.com/leanprover/lean4/pull/${{ steps.workflow-info.outputs.pullRequestNumber }}"
+          fi
+
+      - name: Push changes
+        if: steps.workflow-info.outputs.pullRequestNumber != '' && steps.ready.outputs.mathlib_ready == 'true'
         run: |
           git push origin lean-pr-testing-${{ steps.workflow-info.outputs.pullRequestNumber }}

.github/workflows/pr-title.yml

@@ -0,0 +1,20 @@
+name: Check PR title for commit convention
+
+on:
+  merge_group:
+  pull_request:
+    types: [opened, synchronize, reopened, edited]
+
+jobs:
+  check-pr-title:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check PR title
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const msg = context.payload.pull_request? context.payload.pull_request.title : context.payload.merge_group.head_commit.message;
+            console.log(`Message: ${msg}`)
+            if (!/^(feat|fix|doc|style|refactor|test|chore|perf): .*[^.]($|\n\n)/.test(msg)) {
+              core.setFailed('PR title does not follow the Commit Convention (https://leanprover.github.io/lean4/doc/dev/commit_convention.html).');
+            }

.github/workflows/pr.yml

@@ -1,31 +0,0 @@
-name: sanity-check opened PRs
-
-on:
-  # needs read/write GH token, do *not* execute arbitrary code from PR
-  pull_request_target:
-    types: [opened]
-
-jobs:
-  check-pr:
-    runs-on: ubuntu-latest
-    steps:
-      - name: Check Commit Message
-        uses: actions/github-script@v6
-        with:
-          github-token: ${{ secrets.GITHUB_TOKEN }}
-          script: |
-            const { data: commits } = await github.rest.pulls.listCommits({
-              owner: context.repo.owner,
-              repo: context.repo.repo,
-              pull_number: context.issue.number,
-            });
-            console.log(commits[0].commit.message);
-            // check first commit only (and only once) since later commits might be intended to be squashed away
-            if (!/^(feat|fix|doc|style|refactor|test|chore|perf): .*[^.]($|\n\n)/.test(commits[0].commit.message)) {
-              await github.rest.issues.createComment({
-                owner: context.repo.owner,
-                repo: context.repo.repo,
-                issue_number: context.issue.number,
-                body: 'Thanks for your contribution! Please make sure to follow our [Commit Convention](https://leanprover.github.io/lean4/doc/dev/commit_convention.html).',
-              });
-            }

.github/workflows/update-stage0.yml

@@ -0,0 +1,78 @@
+name: Update stage0
+
+# This action will update stage0 on master as soon as
+# src/stdlib_flags.h and stage0/src/stdlib_flags.h
+# are out of sync there, or when manually triggered.
+# The update bypasses the merge queue to be quick.
+# Also see <doc/dev/bootstrap.md>.
+
+on:
+  push:
+    branches:
+      - 'master'
+  workflow_dispatch:
+
+concurrency:
+  group: stage0
+  cancel-in-progress: true
+
+jobs:
+  update-stage0:
+    runs-on: ubuntu-latest
+    steps:
+    # This action should push to an otherwise protected branch, so it
+    # uses a deploy key with write permissions, as suggested at
+    # https://stackoverflow.com/a/76135647/946226
+    - uses: actions/checkout@v3
+      with:
+        ssh-key: ${{secrets.STAGE0_SSH_KEY}}
+    - run: echo "should_update_stage0=yes" >> "$GITHUB_ENV"
+    - name: Check if automatic update is needed
+      if: github.event_name == 'push'
+      run: |
+        if diff -u src/stdlib_flags.h stage0/src/stdlib_flags.h
+        then
+          echo "src/stdlib_flags.h and stage0/src/stdlib_flags.h agree, nothing to do"
+          echo "should_update_stage0=no" >> "$GITHUB_ENV"
+        fi
+    - name: Setup git user
+      if: env.should_update_stage0 == 'yes'
+      run: |
+          git config --global user.name "Lean stage0 autoupdater"
+          git config --global user.email "<>"
+    # Would be nice, but does not work yet:
+    # https://github.com/DeterminateSystems/magic-nix-cache/issues/39
+    # This action does not run that often and building runs in a few minutes, so ok for now
+    #- if: env.should_update_stage0 == 'yes'
+    #  uses: DeterminateSystems/magic-nix-cache-action@v2
+    - if: env.should_update_stage0 == 'yes'
+      name: Restore Build Cache
+      uses: actions/cache/restore@v3
+      with:
+        path: nix-store-cache
+        key: Nix Linux-nix-store-cache-${{ github.sha }}
+        # fall back to (latest) previous cache
+        restore-keys: |
+          Nix Linux-nix-store-cache
+    - if: env.should_update_stage0 == 'yes'
+      name: Further Set Up Nix Cache
+      shell: bash -euxo pipefail {0}
+      run: |
+        # Nix seems to mutate the cache, so make a copy
+        cp -r nix-store-cache nix-store-cache-copy || true
+    - if: env.should_update_stage0 == 'yes'
+      name: Install Nix
+      uses: DeterminateSystems/nix-installer-action@main
+      with:
+        extra-conf: |
+          substituters = file://${{ github.workspace }}/nix-store-cache-copy?priority=10&trusted=true https://cache.nixos.org  
+    - if: env.should_update_stage0 == 'yes'
+      run: nix run .#update-stage0-commit
+    - if: env.should_update_stage0 == 'yes'
+      run: git show --stat
+    - if: env.should_update_stage0 == 'yes' && github.event_name == 'push'
+      name: Sanity check # to avoid loops
+      run: |
+        diff -u src/stdlib_flags.h stage0/src/stdlib_flags.h || exit 1
+    - if: env.should_update_stage0 == 'yes'
+      run: git push origin

.gitignore

@@ -2,6 +2,8 @@
 \#*
 .#*
 *.lock
+.lake
+lake-manifest.json
 build
 !/src/lake/Lake/Build
 GPATH

.vscode/settings.json

@@ -1,7 +0,0 @@
-{
-    "files.insertFinalNewline": true,
-    "files.trimTrailingWhitespace": true,
-    "[markdown]": {
-        "rewrap.wrappingColumn": 70
-    }
-}

CMakeLists.txt

@@ -11,7 +11,7 @@ foreach(var ${vars})
     list(APPEND STAGE0_ARGS "-D${CMAKE_MATCH_1}=${${var}}")
   elseif("${currentHelpString}" MATCHES "No help, variable specified on the command line." OR "${currentHelpString}" STREQUAL "")
     list(APPEND CL_ARGS "-D${var}=${${var}}")
-    if("${var}" STREQUAL "USE_GMP")
+    if("${var}" MATCHES "USE_GMP|CHECK_OLEAN_VERSION")
       # must forward options that generate incompatible .olean format
       list(APPEND STAGE0_ARGS "-D${var}=${${var}}")
     endif()
@@ -35,6 +35,8 @@ ExternalProject_add(stage0
   SOURCE_SUBDIR src
   BINARY_DIR stage0
   # do not rebuild stage0 when git hash changes; it's not from this commit anyway
+  # (however, `CHECK_OLEAN_VERSION=ON` in CI will override this as we need to
+  # embed the githash into the stage 1 library built by stage 0)
   CMAKE_ARGS -DSTAGE=0 -DUSE_GITHASH=OFF ${PLATFORM_ARGS} ${STAGE0_ARGS}
   BUILD_ALWAYS ON  # cmake doesn't auto-detect changes without a download method
   INSTALL_COMMAND ""  # skip install

CODEOWNERS

@@ -0,0 +1,23 @@
+# Code Owners
+#
+# Documents responsible people per component.
+# Listed persons will automatically be asked by GitHub to review a PR touching these paths.
+# If multiple names are listed, a review by any of them is considered sufficient by default.
+
+/.github/ @Kha @semorrison
+/RELEASES.md @semorrison
+/src/Init/IO.lean @joehendrix
+/src/kernel/ @leodemoura
+/src/lake/ @tydeu
+/src/Lean/Compiler/ @leodemoura
+/src/Lean/Data/Lsp/ @mhuisi
+/src/Lean/Elab/Deriving/ @semorrison
+/src/Lean/Elab/Tactic/ @semorrison
+/src/Lean/Language/ @Kha
+/src/Lean/Meta/Tactic/ @leodemoura
+/src/Lean/Parser/ @Kha
+/src/Lean/PrettyPrinter/ @Kha
+/src/Lean/PrettyPrinter/Delaborator/ @kmill
+/src/Lean/Server/ @mhuisi
+/src/Lean/Widget/ @Vtec234
+/src/runtime/io.cpp @joehendrix

CONTRIBUTING.md

@@ -1,61 +1,79 @@
-# Contribution Guidelines
+External Contribution Guidelines
+============
 
-Thank you for your interest in contributing to Lean! There are many ways to contribute and we appreciate all of them.
+In the past, we accepted most pull requests. This practice produced hard to maintain code, performance problems, and bugs. In order to improve the quality and maintainability of our codebase, we've established the following guidelines for external contributions.
 
-## Bug reports
+Helpful links
+-------
 
-Bug reports as new issues are always welcome. Please check the existing [issues](https://github.com/leanprover/lean4/issues) first.
-Reduce the issue to a self-contained, reproducible test case.
-If you have the chance, before reporting a bug, please search existing issues, as it's possible that
-someone else has already reported your error.
-If you're not sure if something is a bug or not, feel free to file a bug anyway. You may also want to discuss it with the Lean
-community using the [lean4 Zulip channel](https://leanprover.zulipchat.com/#narrow/stream/270676-lean4).
+* [Development Setup](./doc/dev/index.md)
+* [Testing](./doc/dev/testing.md)
+* [Commit convention](./doc/dev/commit_convention.md)
 
-## Simple fixes
+Before You Submit a Pull Request (PR):
+-------
 
-Simple fixes for **typos and clear bugs** are welcome.
+**Start with an Issue**: Before submitting a PR, always open an issue discussing the problem you wish to solve or the feature you'd like to add. Use the prefix `RFC:` (request for comments) if you are proposing a new feature. Ask for feedback from other users. Take the time to summarize all the feedback. This allows the maintainers to evaluate your proposal more efficiently. When creating a RFC, consider the following questions:
 
-# **IMPORTANT**
+  - **User Experience**: How does this feature improve the user experience?
 
-We are currently overwhelmed. We respectfully request that you hold off on submitting Pull Requests and creating Request for Comments (RFCs) at this time. Our team is actively seeking funding to expand the Lean development team and improve our capacity to review and integrate contributions. We appreciate your understanding and look forward to being able to accept contributions in the near future. In the meantime, the process described in the following sections is temporarily suspended.
+  - **Beneficiaries**: Which Lean users and projects do benefit most from this feature/change?
 
-## Documentation
+  - **Community Feedback**: Have you sought feedback or insights from other Lean users?
 
-Tutorial-like examples are very welcome.
-They are useful for finding rough edges and bugs in Lean 4, for highlighting new features, and for showing how to use Lean.
-If you want to store your tutorial in the Lean 4 repository to make sure future changes will not break it, we suggest the following workflow:
-* Contact one of the Lean developers on Zulip, and check whether your tutorial is a good match for the Lean 4 repository.
-* Send bug reports and report rough edges. We will work with you until the tutorial looks great.
-* Add plenty of comments and make sure others will be able to follow it.
-* Create a pull request in the Lean 4 repository. After merging, we will link it to the official documentation and make sure it becomes part of our test suite.
+  - **Maintainability**: Will this change streamline code maintenance or simplify its structure?
 
-You can use `.lean` or `.md` files to create your tutorial. The `.md` files are ideal when you want to format your prose using markdown. For an example, see [this `.md` file](https://github.com/leanprover/lean4/blob/master/doc/lean3changes.md).
+**Understand the Project**: Familiarize yourself with the project, existing issues, and latest commits. Ensure your contribution aligns with the project's direction and priorities.
 
-Contributions to the reference manual are also welcome, but since Lean 4 is changing rapidly, please contact us first using Zulip
-to find out which parts are stable enough to document. We will work with you to get this kind of
-pull request merged. We are also happy to meet using Zoom, Skype or Google hangout to coordinate this kind of effort.
+**Stay Updated**: Regularly fetch and merge changes from the main branch to ensure your branch is up-to-date and can be smoothly integrated.
 
-As Lean 4 matures, other forms of documentation (e.g., doc-strings) will be welcome too.
+**Help wanted**: We have issues tagged with ["help wanted"](https://github.com/leanprover/lean4/issues?q=is%3Aissue+is%3Aopen+label%3A%22help+wanted%22), if you want to contribute to the project, please take a look at them. If you are interested in one of them, post comments, ask questions, and engage with the core developers there.
 
-## "Help wanted"
+Quality Over Quantity:
+-----
 
-For issues marked as [`help wanted`](https://github.com/leanprover/lean4/issues?q=is%3Aissue+is%3Aopen+label%3A%22help+wanted%22), pull requests (PR) are welcome and we will work with you to get a PR merged. Some of these issues are nontrivial. If you are interested, please consider adding comments to the issue and/or messaging the Lean developers in [Zulip](https://leanprover.zulipchat.com/#).
+**Focused Changes**: Each PR should address a single, clearly-defined issue or feature. Avoid making multiple unrelated changes in a single PR.
 
-## Unexpected Pull Requests
+**Write Tests**: Every new feature or bug fix should come with relevant tests. This ensures the robustness and reliability of the contribution.
 
-We have very few core developers, and we cannot review arbitrary pull requests (PRs). Moreover, many features involve subtle tradeoffs, and it may require significant time and energy to even assess a proposed design. We suggest the following workflow:
+**Documentation**: Update relevant documentation, including comments in the code, to explain the logic and reasoning behind your changes.
 
-* First, discuss your idea with the Lean community on Zulip. Ask the community to help collect examples, document the requirements, and detect complications.
-* If there is broad support, create a detailed issue for it on the Lean 4 repository at GitHub, and tag the issue with `RFC`.
-* Ask the community for help documenting the requirements, and for collecting examples and concerns.
-* Wait for one of the core developers to give you a "go ahead". At this point, the core developers will work with you to make sure your PR gets merged.
+Coding Standards:
+----
 
-We don't want to waste your time by you implementing a feature and then us not being able to merge it.
+**Follow the Code Style**: Ensure that your code follows the established coding style of the project.
 
-## How to Contribute
+**Lean on Lean**: Use Lean's built-in features and libraries effectively, avoiding reinventions.
 
-* Always follow the [commit convention](https://lean-lang.org/lean4/doc/dev/commit_convention.html).
-* Follow the style of the surrounding code. When in doubt, look at other files using the particular syntax as well.
-* Make sure your code is documented.
-* New features or bug fixes should come with appropriate tests.
-* Ensure all tests work before submitting a PR; see [Development Setup](https://lean-lang.org/lean4/doc/make/index.html#development-setup) and [Fixing Tests](https://lean-lang.org/lean4/doc/dev/fixing_tests.html).
+**Performance**: Make sure that your changes do not introduce performance regressions. If possible, optimize the solution for speed and resource usage.
+
+PR Submission:
+---
+
+**Descriptive Title and Summary**: The PR title should briefly explain the purpose of the PR. The summary should give more detailed information on what changes are made and why. Links to Zulip threads are not acceptable as a summary. You are responsible for summarizing the discussion, and getting support for it.
+
+**Follow the commit convention**: Pull requests are squash merged, and the
+commit message is taken from the pull request title and body, so make sure they adhere to the [commit convention](https://github.com/leanprover/lean4/blob/master/doc/dev/commit_convention.md). Put questions and extra information, which should not be part of the final commit message, into a first comment rather than the Pull Request description.
+Because the change will be squashed, there is no need to polish the commit messages and history on the branch.
+
+**Link to Relevant Issues**: Reference any issues that your PR addresses to provide context.
+
+**Stay Responsive**: Once the PR is submitted, stay responsive to feedback and be prepared to make necessary revisions. We will close any PR that has been inactive (no response or updates from the submitter) for more than a month.
+
+Reviews and Feedback:
+----
+
+**Be Patient**: Given the limited number of full-time maintainers and the volume of PRs, reviews may take some time.
+
+**Engage Constructively**: Always approach feedback positively and constructively. Remember, reviews are about ensuring the best quality for the project, not personal criticism.
+
+**Continuous Integration**: Ensure that all CI checks pass on your PR. Failed checks will delay the review process. The maintainers will not check PRs containing failures.
+
+What to Expect:
+----
+
+**Not All PRs Get Merged**: While we appreciate every contribution, not all PRs will be merged. Ensure your changes align with the project's goals and quality standards.
+
+**Feedback is a Gift**: It helps improve the project and can also help you grow as a developer or contributor.
+
+**Community Involvement**: Engage with the Lean community on our communication channels. This can lead to better collaboration and understanding of the project's direction.

README.md

@@ -1,20 +1,15 @@
 This is the repository for **Lean 4**.
 
-We provide [nightly releases](https://github.com/leanprover/lean4-nightly/releases)
-and have just begun regular [stable point releases](https://github.com/leanprover/lean4/releases).
-
 # About
 
-- [Quickstart](https://github.com/leanprover/lean4/blob/master/doc/quickstart.md)
-- [Walkthrough installation video](https://www.youtube.com/watch?v=yZo6k48L0VY)
-- [Quick tour video](https://youtu.be/zyXtbb_eYbY)
+- [Quickstart](https://lean-lang.org/lean4/doc/quickstart.html)
 - [Homepage](https://lean-lang.org)
 - [Theorem Proving Tutorial](https://lean-lang.org/theorem_proving_in_lean4/)
 - [Functional Programming in Lean](https://lean-lang.org/functional_programming_in_lean/)
 - [Manual](https://lean-lang.org/lean4/doc/)
 - [Release notes](RELEASES.md) starting at v4.0.0-m3
 - [Examples](https://lean-lang.org/lean4/doc/examples.html)
-- [External Contribution Guidelines](https://github.com/leanprover/lean4/blob/master/doc/contributions.md)
+- [External Contribution Guidelines](CONTRIBUTING.md)
 - [FAQ](https://lean-lang.org/lean4/doc/faq.html)
 
 # Installation

RELEASES.md

@@ -5,13 +5,684 @@ There is not yet a strong guarantee of backwards compatibility between versions,
 only an expectation that breaking changes will be documented in this file.
 
 This file contains work-in-progress notes for the upcoming release, as well as previous stable releases.
-Please check the [releases](https://github.com/leanprover/lean4/releases) page for the current status of each version.
+Please check the [releases](https://github.com/leanprover/lean4/releases) page for the current status
+of each version.
 
-v4.3.0 (development in progress)
+v4.8.0 (development in progress)
+---------
+
+* **Executables configured with `supportInterpreter := true` on Windows should now be run via `lake exe` to function properly.**
+
+  The way Lean is built on Windows has changed (see PR [#3601](https://github.com/leanprover/lean4/pull/3601)). As a result, Lake now dynamically links executables with `supportInterpreter := true` on Windows to `libleanshared.dll` and `libInit_shared.dll`. Therefore, such executables will not run unless those shared libraries are co-located with the executables or part of `PATH`. Running the executable via `lake exe` will ensure these libraries are part of `PATH`.
+
+  In a related change, the signature of the `nativeFacets` Lake configuration options has changed from a static `Array` to a function `(shouldExport : Bool) → Array`. See its docstring or Lake's [README](src/lake/README.md) for further details on the changed option.
+
+* Lean now generates an error if the type of a theorem is **not** a proposition.
+
+* Importing two different files containing proofs of the same theorem is no longer considered an error. This feature is particularly useful for theorems that are automatically generated on demand (e.g., equational theorems).
+
+* New command `derive_functional_induction`:
+
+  Derived from the definition of a (possibly mutually) recursive function
+  defined by well-founded recursion, a **functional induction principle** is
+  tailored to proofs about that function. For example from:
+  ```
+  def ackermann : Nat → Nat → Nat
+    | 0, m => m + 1
+    | n+1, 0 => ackermann n 1
+    | n+1, m+1 => ackermann n (ackermann (n + 1) m)
+  derive_functional_induction ackermann
+  ```
+  we get
+  ```
+  ackermann.induct (motive : Nat → Nat → Prop) (case1 : ∀ (m : Nat), motive 0 m)
+    (case2 : ∀ (n : Nat), motive n 1 → motive (Nat.succ n) 0)
+    (case3 : ∀ (n m : Nat), motive (n + 1) m → motive n (ackermann (n + 1) m) → motive (Nat.succ n) (Nat.succ m))
+    (x x : Nat) : motive x x
+  ```
+
+* The termination checker now recognizes more recursion patterns without an
+  explicit `termination_by`. In particular the idiom of counting up to an upper
+  bound, as in
+  ```
+  def Array.sum (arr : Array Nat) (i acc : Nat) : Nat :=
+    if _ : i < arr.size then
+      Array.sum arr (i+1) (acc + arr[i])
+    else
+      acc
+  ```
+  is recognized without having to say `termination_by arr.size - i`.
+
+* Attribute `@[pp_using_anonymous_constructor]` to make structures pretty print like `⟨x, y, z⟩`
+  rather than `{a := x, b := y, c := z}`.
+  This attribute is applied to `Sigma`, `PSigma`, `PProd`, `Subtype`, `And`, and `Fin`.
+
+* Now structure instances pretty print with parent structures' fields inlined.
+  That is, if `B` extends `A`, then `{ toA := { x := 1 }, y := 2 }` now pretty prints as `{ x := 1, y := 2 }`.
+  Setting option `pp.structureInstances.flatten` to false turns this off.
+
+* Option `pp.structureProjections` is renamed to `pp.fieldNotation`, and there is now a suboption `pp.fieldNotation.generalized`
+  to enable pretty printing function applications using generalized field notation (defaults to true).
+  Field notation can be disabled on a function-by-function basis using the `@[pp_nodot]` attribute.
+
+Breaking changes:
+
+* Automatically generated equational theorems are now named using suffix `.eq_<idx>` instead of `._eq_<idx>`, and `.def` instead of `._unfold`. Example:
+```
+def fact : Nat → Nat
+  | 0 => 1
+  | n+1 => (n+1) * fact n
+
+theorem ex : fact 0 = 1 := by unfold fact; decide
+
+#check fact.eq_1
+-- fact.eq_1 : fact 0 = 1
+
+#check fact.eq_2
+-- fact.eq_2 (n : Nat) : fact (Nat.succ n) = (n + 1) * fact n
+
+#check fact.def
+/-
+fact.def :
+  ∀ (x : Nat),
+    fact x =
+      match x with
+      | 0 => 1
+      | Nat.succ n => (n + 1) * fact n
+-/
+```
+
+* The coercion from `String` to `Name` was removed. Previously, it was `Name.mkSimple`, which does not separate strings at dots, but experience showed that this is not always the desired coercion. For the previous behavior, manually insert a call to `Name.mkSimple`.
+
+v4.7.0
+---------
+
+* `simp` and `rw` now use instance arguments found by unification,
+  rather than always resynthesizing. For backwards compatibility, the original behaviour is
+  available via `set_option tactic.skipAssignedInstances false`.
+  [#3507](https://github.com/leanprover/lean4/pull/3507) and
+  [#3509](https://github.com/leanprover/lean4/pull/3509).
+
+* When the `pp.proofs` is false, now omitted proofs use `⋯` rather than `_`,
+  which gives a more helpful error message when copied from the Infoview.
+  The `pp.proofs.threshold` option lets small proofs always be pretty printed.
+  [#3241](https://github.com/leanprover/lean4/pull/3241).
+
+* `pp.proofs.withType` is now set to false by default to reduce noise in the info view.
+
+* The pretty printer for applications now handles the case of over-application itself when applying app unexpanders.
+  In particular, the ``| `($_ $a $b $xs*) => `(($a + $b) $xs*)`` case of an `app_unexpander` is no longer necessary.
+  [#3495](https://github.com/leanprover/lean4/pull/3495).
+
+* New `simp` (and `dsimp`) configuration option: `zetaDelta`. It is `false` by default.
+  The `zeta` option is still `true` by default, but their meaning has changed.
+  - When `zeta := true`, `simp` and `dsimp` reduce terms of the form
+    `let x := val; e[x]` into `e[val]`.
+  - When `zetaDelta := true`, `simp` and `dsimp` will expand let-variables in
+    the context. For example, suppose the context contains `x := val`. Then,
+    any occurrence of `x` is replaced with `val`.
+
+  See [issue #2682](https://github.com/leanprover/lean4/pull/2682) for additional details. Here are some examples:
+  ```
+  example (h : z = 9) : let x := 5; let y := 4; x + y = z := by
+    intro x
+    simp
+    /-
+    New goal:
+    h : z = 9; x := 5 |- x + 4 = z
+    -/
+    rw [h]
+
+  example (h : z = 9) : let x := 5; let y := 4; x + y = z := by
+    intro x
+    -- Using both `zeta` and `zetaDelta`.
+    simp (config := { zetaDelta := true })
+    /-
+    New goal:
+    h : z = 9; x := 5 |- 9 = z
+    -/
+    rw [h]
+
+  example (h : z = 9) : let x := 5; let y := 4; x + y = z := by
+    intro x
+    simp [x] -- asks `simp` to unfold `x`
+    /-
+    New goal:
+    h : z = 9; x := 5 |- 9 = z
+    -/
+    rw [h]
+
+  example (h : z = 9) : let x := 5; let y := 4; x + y = z := by
+    intro x
+    simp (config := { zetaDelta := true, zeta := false })
+    /-
+    New goal:
+    h : z = 9; x := 5 |- let y := 4; 5 + y = z
+    -/
+    rw [h]
+  ```
+
+* When adding new local theorems to `simp`, the system assumes that the function application arguments
+  have been annotated with `no_index`. This modification, which addresses [issue #2670](https://github.com/leanprover/lean4/issues/2670),
+  restores the Lean 3 behavior that users expect. With this modification, the following examples are now operational:
+  ```
+  example {α β : Type} {f : α × β → β → β} (h : ∀ p : α × β, f p p.2 = p.2)
+    (a : α) (b : β) : f (a, b) b = b := by
+    simp [h]
+
+  example {α β : Type} {f : α × β → β → β}
+    (a : α) (b : β) (h : f (a,b) (a,b).2 = (a,b).2) : f (a, b) b = b := by
+    simp [h]
+  ```
+  In both cases, `h` is applicable because `simp` does not index f-arguments anymore when adding `h` to the `simp`-set.
+  It's important to note, however, that global theorems continue to be indexed in the usual manner.
+
+* Improved the error messages produced by the `decide` tactic. [#3422](https://github.com/leanprover/lean4/pull/3422)
+
+* Improved auto-completion performance. [#3460](https://github.com/leanprover/lean4/pull/3460)
+
+* Improved initial language server startup performance. [#3552](https://github.com/leanprover/lean4/pull/3552)
+
+* Changed call hierarchy to sort entries and strip private header from names displayed in the call hierarchy. [#3482](https://github.com/leanprover/lean4/pull/3482)
+
+* There is now a low-level error recovery combinator in the parsing framework, primarily intended for DSLs. [#3413](https://github.com/leanprover/lean4/pull/3413)
+
+* You can now write `termination_by?` after a declaration to see the automatically inferred
+  termination argument, and turn it into a `termination_by …` clause using the “Try this” widget or a code action. [#3514](https://github.com/leanprover/lean4/pull/3514)
+
+* A large fraction of `Std` has been moved into the Lean repository.
+  This was motivated by:
+  1. Making universally useful tactics such as `ext`, `by_cases`, `change at`,
+    `norm_cast`, `rcases`, `simpa`, `simp?`, `omega`, and `exact?`
+    available to all users of Lean, without imports.
+  2. Minimizing the syntactic changes between plain Lean and Lean with `import Std`.
+  3. Simplifying the development process for the basic data types
+     `Nat`, `Int`, `Fin` (and variants such as `UInt64`), `List`, `Array`,
+     and `BitVec` as we begin making the APIs and simp normal forms for these types
+     more complete and consistent.
+  4. Laying the groundwork for the Std roadmap, as a library focused on
+     essential datatypes not provided by the core langauge (e.g. `RBMap`)
+     and utilities such as basic IO.
+  While we have achieved most of our initial aims in `v4.7.0-rc1`,
+  some upstreaming will continue over the coming months.
+
+* The `/` and `%` notations in `Int` now use `Int.ediv` and `Int.emod`
+  (i.e. the rounding conventions have changed).
+  Previously `Std` overrode these notations, so this is no change for users of `Std`.
+  There is now kernel support for these functions.
+  [#3376](https://github.com/leanprover/lean4/pull/3376).
+
+* `omega`, our integer linear arithmetic tactic, is now availabe in the core langauge.
+  * It is supplemented by a preprocessing tactic `bv_omega` which can solve goals about `BitVec`
+    which naturally translate into linear arithmetic problems.
+    [#3435](https://github.com/leanprover/lean4/pull/3435).
+  * `omega` now has support for `Fin` [#3427](https://github.com/leanprover/lean4/pull/3427),
+    the `<<<` operator [#3433](https://github.com/leanprover/lean4/pull/3433).
+  * During the port `omega` was modified to no longer identify atoms up to definitional equality
+    (so in particular it can no longer prove `id x ≤ x`). [#3525](https://github.com/leanprover/lean4/pull/3525).
+    This may cause some regressions.
+    We plan to provide a general purpose preprocessing tactic later, or an `omega!` mode.
+  * `omega` is now invoked in Lean's automation for termination proofs
+    [#3503](https://github.com/leanprover/lean4/pull/3503) as well as in
+    array indexing proofs [#3515](https://github.com/leanprover/lean4/pull/3515).
+    This automation will be substantially revised in the medium term,
+    and while `omega` does help automate some proofs, we plan to make this much more robust.
+
+* The library search tactics `exact?` and `apply?` that were originally in
+  Mathlib are now available in Lean itself.  These use the implementation using
+  lazy discrimination trees from `Std`, and thus do not require a disk cache but
+  have a slightly longer startup time.  The order used for selection lemmas has
+  changed as well to favor goals purely based on how many terms in the head
+  pattern match the current goal.
+
+* The `solve_by_elim` tactic has been ported from `Std` to Lean so that library
+  search can use it.
+
+* New `#check_tactic` and `#check_simp` commands have been added.  These are
+  useful for checking tactics (particularly `simp`) behave as expected in test
+  suites.
+
+* Previously, app unexpanders would only be applied to entire applications. However, some notations produce
+  functions, and these functions can be given additional arguments. The solution so far has been to write app unexpanders so that they can take an arbitrary number of additional arguments. However this leads to misleading hover information in the Infoview. For example, while `HAdd.hAdd f g 1` pretty prints as `(f + g) 1`, hovering over `f + g` shows `f`. There is no way to fix the situation from within an app unexpander; the expression position for `HAdd.hAdd f g` is absent, and app unexpanders cannot register TermInfo.
+
+  This commit changes the app delaborator to try running app unexpanders on every prefix of an application, from longest to shortest prefix. For efficiency, it is careful to only try this when app delaborators do in fact exist for the head constant, and it also ensures arguments are only delaborated once. Then, in `(f + g) 1`, the `f + g` gets TermInfo registered for that subexpression, making it properly hoverable.
+
+  [#3375](https://github.com/leanprover/lean4/pull/3375)
+
+Breaking changes:
+* `Lean.withTraceNode` and variants got a stronger `MonadAlwaysExcept` assumption to
+  fix trace trees not being built on elaboration runtime exceptions. Instances for most elaboration
+  monads built on `EIO Exception` should be synthesized automatically.
+* The `match ... with.` and `fun.` notations previously in Std have been replaced by
+  `nomatch ...` and `nofun`. [#3279](https://github.com/leanprover/lean4/pull/3279) and [#3286](https://github.com/leanprover/lean4/pull/3286)
+
+
+Other improvements:
+* several bug fixes for `simp`:
+  * we should not crash when `simp` loops [#3269](https://github.com/leanprover/lean4/pull/3269)
+  * `simp` gets stuck on `autoParam` [#3315](https://github.com/leanprover/lean4/pull/3315)
+  * `simp` fails when custom discharger makes no progress [#3317](https://github.com/leanprover/lean4/pull/3317)
+  * `simp` fails to discharge `autoParam` premises even when it can reduce them to `True` [#3314](https://github.com/leanprover/lean4/pull/3314)
+  * `simp?` suggests generated equations lemma names, fixes [#3547](https://github.com/leanprover/lean4/pull/3547) [#3573](https://github.com/leanprover/lean4/pull/3573)
+* fixes for `match` expressions:
+  * fix regression with builtin literals [#3521](https://github.com/leanprover/lean4/pull/3521)
+  * accept `match` when patterns cover all cases of a `BitVec` finite type [#3538](https://github.com/leanprover/lean4/pull/3538)
+  * fix matching `Int` literals [#3504](https://github.com/leanprover/lean4/pull/3504)
+  * patterns containing int values and constructors [#3496](https://github.com/leanprover/lean4/pull/3496)
+* improve `termination_by` error messages [#3255](https://github.com/leanprover/lean4/pull/3255)
+* fix `rename_i` in macros, fixes [#3553](https://github.com/leanprover/lean4/pull/3553) [#3581](https://github.com/leanprover/lean4/pull/3581)
+* fix excessive resource usage in `generalize`, fixes [#3524](https://github.com/leanprover/lean4/pull/3524) [#3575](https://github.com/leanprover/lean4/pull/3575)
+* an equation lemma with autoParam arguments fails to rewrite, fixing [#2243](https://github.com/leanprover/lean4/pull/2243) [#3316](https://github.com/leanprover/lean4/pull/3316)
+* `add_decl_doc` should check that declarations are local [#3311](https://github.com/leanprover/lean4/pull/3311)
+* instantiate the types of inductives with the right parameters, closing [#3242](https://github.com/leanprover/lean4/pull/3242) [#3246](https://github.com/leanprover/lean4/pull/3246)
+* New simprocs for many basic types. [#3407](https://github.com/leanprover/lean4/pull/3407)
+
+Lake fixes:
+* Warn on fetch cloud release failure [#3401](https://github.com/leanprover/lean4/pull/3401)
+* Cloud release trace & `lake build :release` errors [#3248](https://github.com/leanprover/lean4/pull/3248)
+
+v4.6.1
+---------
+* Backport of [#3552](https://github.com/leanprover/lean4/pull/3552) fixing a performance regression
+  in server startup.
+
+v4.6.0
+---------
+
+* Add custom simplification procedures (aka `simproc`s) to `simp`. Simprocs can be triggered by the simplifier on a specified term-pattern. Here is an small example:
+  ```lean
+  import Lean.Meta.Tactic.Simp.BuiltinSimprocs.Nat
+
+  def foo (x : Nat) : Nat :=
+    x + 10
+
+  /--
+  The `simproc` `reduceFoo` is invoked on terms that match the pattern `foo _`.
+  -/
+  simproc reduceFoo (foo _) :=
+    /- A term of type `Expr → SimpM Step -/
+    fun e => do
+      /-
+      The `Step` type has three constructors: `.done`, `.visit`, `.continue`.
+      * The constructor `.done` instructs `simp` that the result does
+        not need to be simplied further.
+      * The constructor `.visit` instructs `simp` to visit the resulting expression.
+      * The constructor `.continue` instructs `simp` to try other simplification procedures.
+
+      All three constructors take a `Result`. The `.continue` contructor may also take `none`.
+      `Result` has two fields `expr` (the new expression), and `proof?` (an optional proof).
+       If the new expression is definitionally equal to the input one, then `proof?` can be omitted or set to `none`.
+      -/
+      /- `simp` uses matching modulo reducibility. So, we ensure the term is a `foo`-application. -/
+      unless e.isAppOfArity ``foo 1 do
+        return .continue
+      /- `Nat.fromExpr?` tries to convert an expression into a `Nat` value -/
+      let some n ← Nat.fromExpr? e.appArg!
+        | return .continue
+      return .done { expr := Lean.mkNatLit (n+10) }
+  ```
+  We disable simprocs support by using the command `set_option simprocs false`. This command is particularly useful when porting files to v4.6.0.
+  Simprocs can be scoped, manually added to `simp` commands, and suppressed using `-`. They are also supported by `simp?`. `simp only` does not execute any `simproc`. Here are some examples for the `simproc` defined above.
+  ```lean
+  example : x + foo 2 = 12 + x := by
+    set_option simprocs false in
+      /- This `simp` command does not make progress since `simproc`s are disabled. -/
+      fail_if_success simp
+    simp_arith
+
+  example : x + foo 2 = 12 + x := by
+    /- `simp only` must not use the default simproc set. -/
+    fail_if_success simp only
+    simp_arith
+
+  example : x + foo 2 = 12 + x := by
+    /-
+    `simp only` does not use the default simproc set,
+    but we can provide simprocs as arguments. -/
+    simp only [reduceFoo]
+    simp_arith
+
+  example : x + foo 2 = 12 + x := by
+    /- We can use `-` to disable `simproc`s. -/
+    fail_if_success simp [-reduceFoo]
+    simp_arith
+  ```
+  The command `register_simp_attr <id>` now creates a `simp` **and** a `simproc` set with the name `<id>`. The following command instructs Lean to insert the `reduceFoo` simplification procedure into the set `my_simp`. If no set is specified, Lean uses the default `simp` set.
+  ```lean
+  simproc [my_simp] reduceFoo (foo _) := ...
+  ```
+
+* The syntax of the `termination_by` and `decreasing_by` termination hints is overhauled:
+
+  * They are now placed directly after the function they apply to, instead of
+    after the whole `mutual` block.
+  * Therefore, the function name no longer has to be mentioned in the hint.
+  * If the function has a `where` clause, the `termination_by` and
+    `decreasing_by` for that function come before the `where`. The
+    functions in the `where` clause can have their own termination hints, each
+    following the corresponding definition.
+  * The `termination_by` clause can only bind “extra parameters”, that are not
+    already bound by the function header, but are bound in a lambda (`:= fun x
+    y z =>`) or in patterns (`| x, n + 1 => …`). These extra parameters used to
+    be understood as a suffix of the function parameters; now it is a prefix.
+
+  Migration guide: In simple cases just remove the function name, and any
+  variables already bound at the header.
+  ```diff
+   def foo : Nat → Nat → Nat := …
+  -termination_by foo a b => a - b
+  +termination_by a b => a - b
+  ```
+  or
+  ```diff
+   def foo : Nat → Nat → Nat := …
+  -termination_by _ a b => a - b
+  +termination_by a b => a - b
+  ```
+
+  If the parameters are bound in the function header (before the `:`), remove them as well:
+  ```diff
+   def foo (a b : Nat) : Nat := …
+  -termination_by foo a b => a - b
+  +termination_by a - b
+  ```
+
+  Else, if there are multiple extra parameters, make sure to refer to the right
+  ones; the bound variables are interpreted from left to right, no longer from
+  right to left:
+  ```diff
+   def foo : Nat → Nat → Nat → Nat
+     | a, b, c => …
+  -termination_by foo b c => b
+  +termination_by a b => b
+  ```
+
+  In the case of a `mutual` block, place the termination arguments (without the
+  function name) next to the function definition:
+  ```diff
+  -mutual
+  -def foo : Nat → Nat → Nat := …
+  -def bar : Nat → Nat := …
+  -end
+  -termination_by
+  -  foo a b => a - b
+  -  bar a => a
+  +mutual
+  +def foo : Nat → Nat → Nat := …
+  +termination_by a b => a - b
+  +def bar : Nat → Nat := …
+  +termination_by a => a
+  +end
+  ```
+
+  Similarly, if you have (mutual) recursion through `where` or `let rec`, the
+  termination hints are now placed directly after the function they apply to:
+  ```diff
+  -def foo (a b : Nat) : Nat := …
+  -  where bar (x : Nat) : Nat := …
+  -termination_by
+  -  foo a b => a - b
+  -  bar x => x
+  +def foo (a b : Nat) : Nat := …
+  +termination_by a - b
+  +  where
+  +    bar (x : Nat) : Nat := …
+  +    termination_by x
+
+  -def foo (a b : Nat) : Nat :=
+  -  let rec bar (x : Nat) :  Nat := …
+  -  …
+  -termination_by
+  -  foo a b => a - b
+  -  bar x => x
+  +def foo (a b : Nat) : Nat :=
+  +  let rec bar (x : Nat) : Nat := …
+  +    termination_by x
+  +  …
+  +termination_by a - b
+  ```
+
+  In cases where a single `decreasing_by` clause applied to multiple mutually
+  recursive functions before, the tactic now has to be duplicated.
+
+* The semantics of `decreasing_by` changed; the tactic is applied to all
+  termination proof goals together, not individually.
+
+  This helps when writing termination proofs interactively, as one can focus
+  each subgoal individually, for example using `·`. Previously, the given
+  tactic script had to work for _all_ goals, and one had to resort to tactic
+  combinators like `first`:
+
+  ```diff
+   def foo (n : Nat) := … foo e1 … foo e2 …
+  -decreasing_by
+  -simp_wf
+  -first | apply something_about_e1; …
+  -      | apply something_about_e2; …
+  +decreasing_by
+  +all_goals simp_wf
+  +· apply something_about_e1; …
+  +· apply something_about_e2; …
+  ```
+
+  To obtain the old behaviour of applying a tactic to each goal individually,
+  use `all_goals`:
+  ```diff
+   def foo (n : Nat) := …
+  -decreasing_by some_tactic
+  +decreasing_by all_goals some_tactic
+  ```
+
+  In the case of mutual recursion each `decreasing_by` now applies to just its
+  function. If some functions in a recursive group do not have their own
+  `decreasing_by`, the default `decreasing_tactic` is used. If the same tactic
+  ought to be applied to multiple functions, the `decreasing_by` clause has to
+  be repeated at each of these functions.
+
+* Modify `InfoTree.context` to facilitate augmenting it with partial contexts while elaborating a command. This breaks backwards compatibility with all downstream projects that traverse the `InfoTree` manually instead of going through the functions in `InfoUtils.lean`, as well as those manually creating and saving `InfoTree`s. See [PR #3159](https://github.com/leanprover/lean4/pull/3159) for how to migrate your code.
+
+* Add language server support for [call hierarchy requests](https://www.youtube.com/watch?v=r5LA7ivUb2c) ([PR #3082](https://github.com/leanprover/lean4/pull/3082)). The change to the .ilean format in this PR means that projects must be fully rebuilt once in order to generate .ilean files with the new format before features like "find references" work correctly again.
+
+* Structure instances with multiple sources (for example `{a, b, c with x := 0}`) now have their fields filled from these sources
+  in strict left-to-right order. Furthermore, the structure instance elaborator now aggressively use sources to fill in subobject
+  fields, which prevents unnecessary eta expansion of the sources,
+  and hence greatly reduces the reliance on costly structure eta reduction. This has a large impact on mathlib,
+  reducing total CPU instructions by 3% and enabling impactful refactors like leanprover-community/mathlib4#8386
+  which reduces the build time by almost 20%.
+  See [PR #2478](https://github.com/leanprover/lean4/pull/2478) and [RFC #2451](https://github.com/leanprover/lean4/issues/2451).
+
+* Add pretty printer settings to omit deeply nested terms (`pp.deepTerms false` and `pp.deepTerms.threshold`) ([PR #3201](https://github.com/leanprover/lean4/pull/3201))
+
+* Add pretty printer options `pp.numeralTypes` and `pp.natLit`.
+  When `pp.numeralTypes` is true, then natural number literals, integer literals, and rational number literals
+  are pretty printed with type ascriptions, such as `(2 : Rat)`, `(-2 : Rat)`, and `(-2 / 3 : Rat)`.
+  When `pp.natLit` is true, then raw natural number literals are pretty printed as `nat_lit 2`.
+  [PR #2933](https://github.com/leanprover/lean4/pull/2933) and [RFC #3021](https://github.com/leanprover/lean4/issues/3021).
+
+Lake updates:
+* improved platform information & control [#3226](https://github.com/leanprover/lean4/pull/3226)
+* `lake update` from unsupported manifest versions [#3149](https://github.com/leanprover/lean4/pull/3149)
+
+Other improvements:
+* make `intro` be aware of `let_fun` [#3115](https://github.com/leanprover/lean4/pull/3115)
+* produce simpler proof terms in `rw` [#3121](https://github.com/leanprover/lean4/pull/3121)
+* fuse nested `mkCongrArg` calls in proofs generated by `simp` [#3203](https://github.com/leanprover/lean4/pull/3203)
+* `induction using` followed by a general term [#3188](https://github.com/leanprover/lean4/pull/3188)
+* allow generalization in `let` [#3060](https://github.com/leanprover/lean4/pull/3060), fixing [#3065](https://github.com/leanprover/lean4/issues/3065)
+* reducing out-of-bounds `swap!` should return `a`, not `default`` [#3197](https://github.com/leanprover/lean4/pull/3197), fixing [#3196](https://github.com/leanprover/lean4/issues/3196)
+* derive `BEq` on structure with `Prop`-fields [#3191](https://github.com/leanprover/lean4/pull/3191), fixing [#3140](https://github.com/leanprover/lean4/issues/3140)
+* refine through more `casesOnApp`/`matcherApp` [#3176](https://github.com/leanprover/lean4/pull/3176), fixing [#3175](https://github.com/leanprover/lean4/pull/3175)
+* do not strip dotted components from lean module names [#2994](https://github.com/leanprover/lean4/pull/2994), fixing [#2999](https://github.com/leanprover/lean4/issues/2999)
+* fix `deriving` only deriving the first declaration for some handlers [#3058](https://github.com/leanprover/lean4/pull/3058), fixing [#3057](https://github.com/leanprover/lean4/issues/3057)
+* do not instantiate metavariables in kabstract/rw for disallowed occurrences [#2539](https://github.com/leanprover/lean4/pull/2539), fixing [#2538](https://github.com/leanprover/lean4/issues/2538)
+* hover info for `cases h : ...` [#3084](https://github.com/leanprover/lean4/pull/3084)
+
+v4.5.0
+---------
+
+* Modify the lexical syntax of string literals to have string gaps, which are escape sequences of the form `"\" newline whitespace*`.
+  These have the interpetation of an empty string and allow a string to flow across multiple lines without introducing additional whitespace.
+  The following is equivalent to `"this is a string"`.
+  ```lean
+  "this is \
+     a string"
+  ```
+  [PR #2821](https://github.com/leanprover/lean4/pull/2821) and [RFC #2838](https://github.com/leanprover/lean4/issues/2838).
+
+* Add raw string literal syntax. For example, `r"\n"` is equivalent to `"\\n"`, with no escape processing.
+  To include double quote characters in a raw string one can add sufficiently many `#` characters before and after
+  the bounding `"`s, as in `r#"the "the" is in quotes"#` for `"the \"the\" is in quotes"`.
+  [PR #2929](https://github.com/leanprover/lean4/pull/2929) and [issue #1422](https://github.com/leanprover/lean4/issues/1422).
+
+* The low-level `termination_by'` clause is no longer supported.
+
+  Migration guide: Use `termination_by` instead, e.g.:
+  ```diff
+  -termination_by' measure (fun ⟨i, _⟩ => as.size - i)
+  +termination_by i _ => as.size - i
+  ```
+
+  If the well-founded relation you want to use is not the one that the
+  `WellFoundedRelation` type class would infer for your termination argument,
+  you can use `WellFounded.wrap` from the std libarary to explicitly give one:
+  ```diff
+  -termination_by' ⟨r, hwf⟩
+  +termination_by x => hwf.wrap x
+  ```
+
+* Support snippet edits in LSP `TextEdit`s. See `Lean.Lsp.SnippetString` for more details.
+
+* Deprecations and changes in the widget API.
+  - `Widget.UserWidgetDefinition` is deprecated in favour of `Widget.Module`. The annotation `@[widget]` is deprecated in favour of `@[widget_module]`. To migrate a definition of type `UserWidgetDefinition`, remove the `name` field and replace the type with `Widget.Module`. Removing the `name` results in a title bar no longer being drawn above your panel widget. To add it back, draw it as part of the component using `<details open=true><summary class='mv2 pointer'>{name}</summary>{rest_of_widget}</details>`. See an example migration [here](https://github.com/leanprover/std4/pull/475/files#diff-857376079661a0c28a53b7ff84701afabbdf529836a6944d106c5294f0e68109R43-R83).
+  - The new command `show_panel_widgets` allows displaying always-on and locally-on panel widgets.
+  - `RpcEncodable` widget props can now be stored in the infotree.
+  - See [RFC 2963](https://github.com/leanprover/lean4/issues/2963) for more details and motivation.
+
+* If no usable lexicographic order can be found automatically for a termination proof, explain why.
+  See [feat: GuessLex: if no measure is found, explain why](https://github.com/leanprover/lean4/pull/2960).
+
+* Option to print [inferred termination argument](https://github.com/leanprover/lean4/pull/3012).
+  With `set_option showInferredTerminationBy true` you will get messages like
+  ```
+  Inferred termination argument:
+  termination_by
+  ackermann n m => (sizeOf n, sizeOf m)
+  ```
+  for automatically generated `termination_by` clauses.
+
+* More detailed error messages for [invalid mutual blocks](https://github.com/leanprover/lean4/pull/2949).
+
+* [Multiple](https://github.com/leanprover/lean4/pull/2923) [improvements](https://github.com/leanprover/lean4/pull/2969) to the output of `simp?` and `simp_all?`.
+
+* Tactics with `withLocation *` [no longer fail](https://github.com/leanprover/lean4/pull/2917) if they close the main goal.
+
+* Implementation of a `test_extern` command for writing tests for `@[extern]` and `@[implemented_by]` functions.
+  Usage is
+  ```
+  import Lean.Util.TestExtern
+
+  test_extern Nat.add 17 37
+  ```
+  The head symbol must be the constant with the `@[extern]` or `@[implemented_by]` attribute. The return type must have a `DecidableEq` instance.
+
+Bug fixes for
+[#2853](https://github.com/leanprover/lean4/issues/2853), [#2953](https://github.com/leanprover/lean4/issues/2953), [#2966](https://github.com/leanprover/lean4/issues/2966),
+[#2971](https://github.com/leanprover/lean4/issues/2971), [#2990](https://github.com/leanprover/lean4/issues/2990), [#3094](https://github.com/leanprover/lean4/issues/3094).
+
+Bug fix for [eager evaluation of default value](https://github.com/leanprover/lean4/pull/3043) in `Option.getD`.
+Avoid [panic in `leanPosToLspPos`](https://github.com/leanprover/lean4/pull/3071) when file source is unavailable.
+Improve [short-circuiting behavior](https://github.com/leanprover/lean4/pull/2972) for `List.all` and `List.any`.
+
+Several Lake bug fixes: [#3036](https://github.com/leanprover/lean4/issues/3036), [#3064](https://github.com/leanprover/lean4/issues/3064), [#3069](https://github.com/leanprover/lean4/issues/3069).
+
+v4.4.0
+---------
+
+* Lake and the language server now support per-package server options using the `moreServerOptions` config field, as well as options that apply to both the language server and `lean` using the `leanOptions` config field. Setting either of these fields instead of `moreServerArgs` ensures that viewing files from a dependency uses the options for that dependency. Additionally, `moreServerArgs` is being deprecated in favor of the `moreGlobalServerArgs` field. See PR [#2858](https://github.com/leanprover/lean4/pull/2858).
+
+  A Lakefile with the following deprecated package declaration:
+  ```lean
+  def moreServerArgs := #[
+    "-Dpp.unicode.fun=true"
+  ]
+  def moreLeanArgs := moreServerArgs
+
+  package SomePackage where
+    moreServerArgs := moreServerArgs
+    moreLeanArgs := moreLeanArgs
+  ```
+
+  ... can be updated to the following package declaration to use per-package options:
+  ```lean
+  package SomePackage where
+    leanOptions := #[⟨`pp.unicode.fun, true⟩]
+  ```
+* [Rename request handler](https://github.com/leanprover/lean4/pull/2462).
+* [Import auto-completion](https://github.com/leanprover/lean4/pull/2904).
+* [`pp.beta`` to apply beta reduction when pretty printing](https://github.com/leanprover/lean4/pull/2864).
+* [Embed and check githash in .olean](https://github.com/leanprover/lean4/pull/2766).
+* [Guess lexicographic order for well-founded recursion](https://github.com/leanprover/lean4/pull/2874).
+* [Allow trailing comma in tuples, lists, and tactics](https://github.com/leanprover/lean4/pull/2643).
+
+Bug fixes for [#2628](https://github.com/leanprover/lean4/issues/2628), [#2883](https://github.com/leanprover/lean4/issues/2883),
+[#2810](https://github.com/leanprover/lean4/issues/2810), [#2925](https://github.com/leanprover/lean4/issues/2925), and [#2914](https://github.com/leanprover/lean4/issues/2914).
+
+**Lake:**
+
+* `lake init .` and a bare `lake init` and will now use the current directory as the package name. [#2890](https://github.com/leanprover/lean4/pull/2890)
+* `lake new` and `lake init` will now produce errors on invalid package names such as `..`, `foo/bar`, `Init`, `Lean`, `Lake`, and `Main`. See issue [#2637](https://github.com/leanprover/lean4/issues/2637) and PR [#2890](https://github.com/leanprover/lean4/pull/2890).
+* `lean_lib` no longer converts its name to upper camel case (e.g., `lean_lib bar` will include modules named `bar.*` rather than `Bar.*`). See issue [#2567](https://github.com/leanprover/lean4/issues/2567) and PR [#2889](https://github.com/leanprover/lean4/pull/2889).
+* Lean and Lake now properly support non-identifier library names (e.g., `lake new 123-hello` and `import «123Hello»` now work correctly). See issue [#2865](https://github.com/leanprover/lean4/issues/2865) and PR [#2889](https://github.com/leanprover/lean4/pull/2888).
+* Lake now filters the environment extensions loaded from a compiled configuration (`lakefile.olean`) to include only those relevant to Lake's workspace loading process. This resolves segmentation faults caused by environment extension type mismatches (e.g., when defining custom elaborators via `elab` in configurations). See issue [#2632](https://github.com/leanprover/lean4/issues/2632) and PR [#2896](https://github.com/leanprover/lean4/pull/2896).
+* Cloud releases will now properly be re-unpacked if the build directory is removed. See PR [#2928](https://github.com/leanprover/lean4/pull/2928).
+* Lake's `math` template has been simplified. See PR [#2930](https://github.com/leanprover/lean4/pull/2930).
+* `lake exe <target>` now parses `target` like a build target (as the help text states it should) rather than as a basic name. For example, `lake exe @mathlib/runLinter` should now work. See PR [#2932](https://github.com/leanprover/lean4/pull/2932).
+* `lake new foo.bar [std]` now generates executables named `foo-bar` and `lake new foo.bar exe` properly creates `foo/bar.lean`. See PR [#2932](https://github.com/leanprover/lean4/pull/2932).
+* Later packages and libraries in the dependency tree are now preferred over earlier ones. That is, the later ones "shadow" the earlier ones. Such an ordering is more consistent with how declarations generally work in programming languages. This will break any package that relied on the previous ordering. See issue [#2548](https://github.com/leanprover/lean4/issues/2548) and PR [#2937](https://github.com/leanprover/lean4/pull/2937).
+* Executable roots are no longer mistakenly treated as importable. They will no longer be picked up by `findModule?`. See PR [#2937](https://github.com/leanprover/lean4/pull/2937).
+
+v4.3.0
+---------
+
+* `simp [f]` does not unfold partial applications of `f` anymore. See issue [#2042](https://github.com/leanprover/lean4/issues/2042).
+  To fix proofs affected by this change, use `unfold f` or `simp (config := { unfoldPartialApp := true }) [f]`.
+* By default, `simp` will no longer try to use Decidable instances to rewrite terms. In particular, not all decidable goals will be closed by `simp`, and the `decide` tactic may be useful in such cases. The `decide` simp configuration option can be used to locally restore the old `simp` behavior, as in `simp (config := {decide := true})`; this includes using Decidable instances to verify side goals such as numeric inequalities.
+
+* Many bug fixes:
+  * [Add left/right actions to term tree coercion elaborator and make `^`` a right action](https://github.com/leanprover/lean4/pull/2778)
+  * [Fix for #2775, don't catch max recursion depth errors](https://github.com/leanprover/lean4/pull/2790)
+  * [Reduction of `Decidable` instances very slow when using `cases` tactic](https://github.com/leanprover/lean4/issues/2552)
+  * [`simp` not rewriting in binder](https://github.com/leanprover/lean4/issues/1926)
+  * [`simp` unfolding `let` even with `zeta := false` option](https://github.com/leanprover/lean4/issues/2669)
+  * [`simp` (with beta/zeta disabled) and discrimination trees](https://github.com/leanprover/lean4/issues/2281)
+  * [unknown free variable introduced by `rw ... at h`](https://github.com/leanprover/lean4/issues/2711)
+  * [`dsimp` doesn't use `rfl` theorems which consist of an unapplied constant](https://github.com/leanprover/lean4/issues/2685)
+  * [`dsimp` does not close reflexive equality goals if they are wrapped in metadata](https://github.com/leanprover/lean4/issues/2514)
+  * [`rw [h]` uses `h` from the environment in preference to `h` from the local context](https://github.com/leanprover/lean4/issues/2729)
+  * [missing `withAssignableSyntheticOpaque` for `assumption` tactic](https://github.com/leanprover/lean4/issues/2361)
+  * [ignoring default value for field warning](https://github.com/leanprover/lean4/issues/2178)
+* [Cancel outstanding tasks on document edit in the language server](https://github.com/leanprover/lean4/pull/2648).
+* [Remove unnecessary `%` operations in `Fin.mod` and `Fin.div`](https://github.com/leanprover/lean4/pull/2688)
+* [Avoid `DecidableEq` in `Array.mem`](https://github.com/leanprover/lean4/pull/2774)
+* [Ensure `USize.size` unifies with `?m + 1`](https://github.com/leanprover/lean4/issues/1926)
+* [Improve compatibility with emacs eglot client](https://github.com/leanprover/lean4/pull/2721)
+
+**Lake:**
+
+* [Sensible defaults for `lake new MyProject math`](https://github.com/leanprover/lean4/pull/2770)
+* Changed `postUpdate?` configuration option to a `post_update` declaration. See the `post_update` syntax docstring for more information on the new syntax.
+* [A manifest is automatically created on workspace load if one does not exists.](https://github.com/leanprover/lean4/pull/2680).
+* The `:=` syntax for configuration declarations (i.e., `package`, `lean_lib`, and `lean_exe`) has been deprecated. For example, `package foo := {...}` is deprecated.
+* [support for overriding package URLs via `LAKE_PKG_URL_MAP`](https://github.com/leanprover/lean4/pull/2709)
+* Moved the default build directory (e.g., `build`), default packages directory (e.g., `lake-packages`), and the compiled configuration (e.g., `lakefile.olean`) into a new dedicated directory for Lake outputs, `.lake`. The cloud release build archives are also stored here, fixing [#2713](https://github.com/leanprover/lean4/issues/2713).
+* Update manifest format to version 7 (see [lean4#2801](https://github.com/leanprover/lean4/pull/2801) for details on the changes).
+* Deprecate the `manifestFile` field of a package configuration.
+* There is now a more rigorous check on `lakefile.olean` compatibility (see [#2842](https://github.com/leanprover/lean4/pull/2842) for more details).
+
+v4.2.0
 ---------
 
 * [isDefEq cache for terms not containing metavariables.](https://github.com/leanprover/lean4/pull/2644).
-* [Cancel outstanding tasks on document edit in the language server](https://github.com/leanprover/lean4/pull/2648).
 * Make [`Environment.mk`](https://github.com/leanprover/lean4/pull/2604) and [`Environment.add`](https://github.com/leanprover/lean4/pull/2642) private, and add [`replay`](https://github.com/leanprover/lean4/pull/2617) as a safer alternative.
 * `IO.Process.output` no longer inherits the standard input of the caller.
 * [Do not inhibit caching](https://github.com/leanprover/lean4/pull/2612) of default-level `match` reduction.
@@ -20,10 +691,6 @@ v4.3.0 (development in progress)
 * [Show path of failed import in Lake](https://github.com/leanprover/lean4/pull/2616).
 * [Fix linker warnings on macOS](https://github.com/leanprover/lean4/pull/2598).
 * **Lake:** Add `postUpdate?` package configuration option. Used by a package to specify some code which should be run after a successful `lake update` of the package or one of its downstream dependencies. ([lake#185](https://github.com/leanprover/lake/issues/185))
-
-v4.2.0
----------
-
 * Improvements to Lake startup time ([#2572](https://github.com/leanprover/lean4/pull/2572), [#2573](https://github.com/leanprover/lean4/pull/2573))
 * `refine e` now replaces the main goal with metavariables which were created during elaboration of `e` and no longer captures pre-existing metavariables that occur in `e` ([#2502](https://github.com/leanprover/lean4/pull/2502)).
   * This is accomplished via changes to `withCollectingNewGoalsFrom`, which also affects `elabTermWithHoles`, `refine'`, `calc` (tactic), and `specialize`. Likewise, all of these now only include newly-created metavariables in their output.

default.nix

@@ -1,9 +0,0 @@
-# used for `nix-shell https://github.com/leanprover/lean4/archive/master.tar.gz -A nix`
-{ nix = (import ./shell.nix {}).nix; } //
-(import (
-  fetchTarball {
-    url = "https://github.com/edolstra/flake-compat/archive/c75e76f80c57784a6734356315b306140646ee84.tar.gz";
-    sha256 = "071aal00zp2m9knnhddgr2wqzlx6i6qa1263lv1y7bdn2w20h10h"; }
-) {
-  src =  ./.;
-}).defaultNix

doc/SUMMARY.md

@@ -4,7 +4,6 @@
 - [Tour of Lean](./tour.md)
 - [Setting Up Lean](./quickstart.md)
   - [Extended Setup Notes](./setup.md)
-  - [Nix Setup](./setup/nix.md)
 - [Theorem Proving in Lean](./tpil.md)
 - [Functional Programming in Lean](fplean.md)
 - [Examples](./examples.md)
@@ -86,10 +85,10 @@
   - [macOS Setup](./make/osx-10.9.md)
   - [Windows MSYS2 Setup](./make/msys2.md)
   - [Windows with WSL](./make/wsl.md)
-  - [Nix Setup (*Experimental*)](./make/nix.md)
 - [Bootstrapping](./dev/bootstrap.md)
 - [Testing](./dev/testing.md)
 - [Debugging](./dev/debugging.md)
 - [Commit Convention](./dev/commit_convention.md)
+- [Release checklist](./dev/release_checklist.md)
 - [Building This Manual](./dev/mdbook.md)
 - [Foreign Function Interface](./dev/ffi.md)

doc/contributions.md

@@ -1,68 +0,0 @@
-External Contribution Guidelines
-============
-
-**In the past, we accepted most pull requests. This practice produced hard to maintain code, performance problems, and bugs.** In order to improve the quality and maintainability of our codebase, we've established the following guidelines for external contributions.
-
-Before You Submit a Pull Request (PR):
--------
-
-**Start with an Issue**: Before submitting a PR, always open an issue discussing the problem you wish to solve or the feature you'd like to add. Use the prefix `RFC:` (request for comments) if you are proposing a new feature. Ask for feedback from other users. Take the time to summarize all the feedback. This allows the maintainers to evaluate your proposal more efficiently. When creating a RFC, consider the following questions:
-
-  - **User Experience**: How does this feature improve the user experience?
-
-  - **Beneficiaries**: Which Lean users and projects do benefit most from this feature/change?
-
-  - **Community Feedback**: Have you sought feedback or insights from other Lean users?
-
-  - **Maintainability**: Will this change streamline code maintenance or simplify its structure?
-
-**Understand the Project**: Familiarize yourself with the project, existing issues, and latest commits. Ensure your contribution aligns with the project's direction and priorities.
-
-**Stay Updated**: Regularly fetch and merge changes from the main branch to ensure your branch is up-to-date and can be smoothly integrated.
-
-**Help wanted**: We have issues tagged with ["help wanted"](https://github.com/leanprover/lean4/issues?q=is%3Aissue+is%3Aopen+label%3A%22help+wanted%22), if you want to contribute to the project, please take a look at them. If you are interested in one of them, post comments, ask questions, and engage with the core developers there.
-
-Quality Over Quantity:
------
-
-**Focused Changes**: Each PR should address a single, clearly-defined issue or feature. Avoid making multiple unrelated changes in a single PR.
-
-**Write Tests**: Every new feature or bug fix should come with relevant tests. This ensures the robustness and reliability of the contribution.
-
-**Documentation**: Update relevant documentation, including comments in the code, to explain the logic and reasoning behind your changes.
-
-Coding Standards:
-----
-
-**Follow the Code Style**: Ensure that your code follows the established coding style of the project.
-
-**Lean on Lean**: Use Lean's built-in features and libraries effectively, avoiding reinventions.
-
-**Performance**: Make sure that your changes do not introduce performance regressions. If possible, optimize the solution for speed and resource usage.
-
-PR Submission:
----
-
-**Descriptive Title and Summary**: The PR title should briefly explain the purpose of the PR. The summary should give more detailed information on what changes are made and why. Links to Zulip threads are not acceptable as a summary. You are responsible for summarizing the discussion, and getting support for it.
-
-**Link to Relevant Issues**: Reference any issues that your PR addresses to provide context.
-
-**Stay Responsive**: Once the PR is submitted, stay responsive to feedback and be prepared to make necessary revisions. We will close any PR that has been inactive (no response or updates from the submitter) for more than a month.
-
-Reviews and Feedback:
-----
-
-**Be Patient**: Given the limited number of full-time maintainers and the volume of PRs, reviews may take some time.
-
-**Engage Constructively**: Always approach feedback positively and constructively. Remember, reviews are about ensuring the best quality for the project, not personal criticism.
-
-**Continuous Integration**: Ensure that all CI checks pass on your PR. Failed checks will delay the review process. The maintainers will not check PRs containing failures.
-
-What to Expect:
-----
-
-**Not All PRs Get Merged**: While we appreciate every contribution, not all PRs will be merged. Ensure your changes align with the project's goals and quality standards.
-
-**Feedback is a Gift**: It helps improve the project and can also help you grow as a developer or contributor.
-
-**Community Involvement**: Engage with the Lean community on our communication channels. This can lead to better collaboration and understanding of the project's direction.

doc/declarations.md

@@ -483,7 +483,43 @@ def baz : Char → Nat
 | _   => 3
 ```
 
-If any of the terms ``tᵢ`` in the template above contain a recursive call to ``foo``, the equation compiler tries to interpret the definition as a structural recursion. In order for that to succeed, the recursive arguments must be subterms of the corresponding arguments on the left-hand side. The function is then defined using a *course of values* recursion, using automatically generated functions ``below`` and ``brec`` in the namespace corresponding to the inductive type of the recursive argument. In this case the defining equations hold definitionally, possibly with additional case splits.
+The case where patterns are matched against an argument whose type is an inductive family is known as *dependent pattern matching*. This is more complicated, because the type of the function being defined can impose constraints on the patterns that are matched. In this case, the equation compiler will detect inconsistent cases and rule them out.
+
+```lean
+universe u
+
+inductive Vector (α : Type u) : Nat → Type u
+  | nil  : Vector α 0
+  | cons : α → Vector α n → Vector α (n+1)
+
+namespace Vector
+
+def head : Vector α (n+1) → α
+  | cons h t => h
+
+def tail : Vector α (n+1) → Vector α n
+  | cons h t => t
+
+def map (f : α → β → γ) : Vector α n → Vector β n → Vector γ n
+  | nil, nil => nil
+  | cons a va, cons b vb => cons (f a b) (map f va vb)
+
+end Vector
+```
+
+.. _recursive_functions:
+
+Recursive functions
+===================
+
+Lean must ensure that a recursive function terminates, for which there are two strategies: _structural recursion_, in which all recursive calls are made on smaller parts of the input data, and _well-founded recursion_, in which recursive calls are justified by showing that arguments to recursive calls are smaller according to some other measure.
+
+Structural recursion
+--------------------
+
+If the definition of a function contains recursive calls, Lean first tries to interpret the definition as a structural recursion. In order for that to succeed, the recursive arguments must be subterms of the corresponding arguments on the left-hand side.
+
+The function is then defined using a *course of values* recursion, using automatically generated functions ``below`` and ``brec`` in the namespace corresponding to the inductive type of the recursive argument. In this case the defining equations hold definitionally, possibly with additional case splits.
 
 ```lean
 namespace Hide
@@ -504,7 +540,12 @@ example : append [(1 : Nat), 2, 3] [4, 5] = [1, 2, 3, 4, 5] => rfl
 end Hide
 ```
 
-If structural recursion fails, the equation compiler falls back on well-founded recursion. It tries to infer an instance of ``SizeOf`` for the type of each argument, and then show that each recursive call is decreasing under the lexicographic order of the arguments with respect to ``sizeOf`` measure. If it fails, the error message provides information as to the goal that Lean tried to prove. Lean uses information in the local context, so you can often provide the relevant proof manually using ``have`` in the body of the definition. In this case of well-founded recursion, the defining equations hold only propositionally, and can be accessed using ``simp`` and ``rewrite`` with the name ``foo``.
+Well-founded recursion
+---------------------
+
+If structural recursion fails, the equation compiler falls back on well-founded recursion. It tries to infer an instance of ``SizeOf`` for the type of each argument, and then tries to find a permutation of the arguments such that each recursive call is decreasing under the lexicographic order with respect to ``sizeOf`` measures.  Lean uses information in the local context, so you can often provide the relevant proof manually using ``have`` in the body of the definition.
+
+In the case of well-founded recursion, the equation used to declare the function holds only propositionally, but not definitionally, and can be accessed using ``unfold``, ``simp`` and ``rewrite`` with the function name (for example ``unfold foo`` or ``simp [foo]``, where ``foo`` is the function defined with well-founded recursion).
 
 ```lean
 namespace Hide
@@ -528,9 +569,53 @@ by rw [div]; rfl
 end Hide
 ```
 
+If Lean cannot find a permutation of the arguments for which all recursive calls are decreasing, it will print a table that contains, for every recursive call, which arguments Lean could prove to be decreasing. For example, a function with three recursive calls and four parameters might cause the following message to be printed
+
+```
+example.lean:37:0-43:31: error: Could not find a decreasing measure.
+The arguments relate at each recursive call as follows:
+(<, ≤, =: relation proved, ? all proofs failed, _: no proof attempted)
+           x1 x2 x3 x4
+1) 39:6-27  =  =  _  =
+2) 40:6-25  =  ?  _  <
+3) 41:6-25  <  _  _  _
+Please use `termination_by` to specify a decreasing measure.
+```
+
+This table should be read as follows:
+
+ * In the first recursive call, in line 39, arguments 1, 2 and 4 are equal to the function's parameters.
+ * The second recursive call, in line 40, has an equal first argument, a smaller fourth argument, and nothing could be inferred for the second argument.
+ * The third recursive call, in line 41, has a decreasing first argument.
+ * No other proofs were attempted, either because the parameter has a type without a non-trivial ``WellFounded`` instance (parameter 3), or because it is already clear that no decreasing measure can be found.
+
+
+Lean will print the termination argument it found if ``set_option showInferredTerminationBy true`` is set.
+
+If Lean does not find the termination argument, or if you want to be explicit, you can append a `termination_by` clause to the function definition, after the function's body, but before the `where` clause if present. It is of the form
+```
+termination_by e
+```
+where ``e`` is an expression that depends on the parameters of the function and should be decreasing at each recursive call. The type of `e` should be an instance of the class ``WellFoundedRelation``, which determines how to compare two values of that type.
+
+If ``f`` has parameters “after the ``:``” (for example when defining functions via patterns using `|`), then these can be brought into scope using the syntax
+```
+termination_by a₁ … aₙ => e
+```
+
+By default, Lean uses the tactic ``decreasing_tactic`` when proving that an argument is decreasing; see its documentation for how to globally extend it. You can also choose to use a different tactic for a given function definition with the clause
+```
+decreasing_by <tac>
+```
+which should come after ``termination_by`, if present.
+
+
 Note that recursive definitions can in general require nested recursions, that is, recursion on different arguments of ``foo`` in the template above. The equation compiler handles this by abstracting later arguments, and recursively defining higher-order functions to meet the specification.
 
-The equation compiler also allows mutual recursive definitions, with a syntax similar to that of [Mutual and Nested Inductive Definitions](#mutual-and-nested-inductive-definitions). They are compiled using well-founded recursion, and so once again the defining equations hold only propositionally.
+Mutual recursion
+----------------
+
+The equation compiler also allows mutual recursive definitions, with a syntax similar to that of [Mutual and Nested Inductive Definitions](#mutual-and-nested-inductive-definitions). Mutual definitions are always compiled using well-founded recursion, and so once again the defining equations hold only propositionally.
 
 ```lean
 mutual
@@ -587,29 +672,31 @@ def num_consts_lst : List Term → Nat
 end
 ```
 
-The case where patterns are matched against an argument whose type is an inductive family is known as *dependent pattern matching*. This is more complicated, because the type of the function being defined can impose constraints on the patterns that are matched. In this case, the equation compiler will detect inconsistent cases and rule them out.
+In a set of mutually recursive function, either all or no functions must have an explicit termination argument (``termination_by``). A change of the default termination tactic (``decreasing_by``) only affects the proofs about the recursive calls of that function, not the other functions in the group.
 
-```lean
-universe u
+```
+mutual
+theorem even_of_odd_succ : ∀ n, Odd (n + 1) → Even n
+| _, odd_succ n h => h
+termination_by n h => h
+decreasing_by decreasing_tactic
 
-inductive Vector (α : Type u) : Nat → Type u
-| nil  : Vector α 0
-| cons : α → Vector α n → Vector α (n+1)
+theorem odd_of_even_succ : ∀ n, Even (n + 1) → Odd n
+| _, even_succ n h => h
+termination_by n h => h
+end
+```
 
-namespace Vector
+Another way to express mutual recursion is using local function definitions in ``where`` or ``let rec`` clauses: these can be mutually recursive with each other and their containing function:
 
-def head {α : Type} : Vector α (n+1) → α
-| cons h t => h
-
-def tail {α : Type} : Vector α (n+1) → Vector α n
-| cons h t => t
-
-def map {α β γ : Type} (f : α → β → γ) :
-  ∀ {n}, Vector α n → Vector β n → Vector γ n
-| 0,   nil,       nil       => nil
-| n+1, cons a va, cons b vb => cons (f a b) (map f va vb)
-
-end Vector
+```
+theorem even_of_odd_succ : ∀ n, Odd (n + 1) → Even n
+  | _, odd_succ n h => h
+termination_by n h => h
+  where
+    theorem odd_of_even_succ : ∀ n, Even (n + 1) → Odd n
+      | _, even_succ n h => h
+    termination_by n h => h
 ```
 
 .. _match_expressions:

doc/dev/bootstrap.md

@@ -65,16 +65,36 @@ You now have a Lean binary and library that include your changes, though their
 own compilation was not influenced by them, that you can use to test your
 changes on test programs whose compilation *will* be influenced by the changes.
 
-Finally, when we want to use new language features in the library, we need to
-update the stage 0 compiler, which can be done via `make -C stageN update-stage0`.
-`make update-stage0` without `-C` defaults to stage1.
+## Updating stage0
 
-Updates to `stage0` should be their own commits in the Git history. In
-other words, before running `make update-stage0`, please commit your
-work. Then, commit the updated `stage0` compiler code with the commit message:
+Finally, when we want to use new language features in the library, we need to
+update the archived C source code of the stage 0 compiler in `stage0/src`.
+
+The github repository will automatically update stage0 on `master` once
+`src/stdlib_flags.h` and `stage0/src/stdlib_flags.h` are out of sync.
+
+If you have write access to the lean4 repository, you can also also manually
+trigger that process, for example to be able to use new features in the compiler itself.
+You can do that on <https://github.com/nomeata/lean4/actions/workflows/update-stage0.yml>
+or using Github CLI with
+```
+gh workflow run update-stage0.yml
+```
+
+Leaving stage0 updates to the CI automation is preferrable, but should you need
+to do it locally, you can use `make update-stage0` in `build/release`, to
+update `stage0` from `stage1`, `make -C stageN update-stage0` to update from
+another stage, or `nix run .#update-stage0-commit` to update using nix.
+
+Updates to `stage0` should be their own commits in the Git history. So should
+you have to include the stage0 update in your PR (rather than using above
+automation after merging changes), commit your work before running `make
+update-stage0`, commit the updated `stage0` compiler code with the commit
+message:
 ```
 chore: update stage0
 ```
+and coordinate with the admins to not squash your PR.
 
 ## Further Bootstrapping Complications
 

doc/dev/commit_convention.md

@@ -1,10 +1,15 @@
 Git Commit Convention
 =====================
 
-We are using the following convention for writing git-commit messages.
-It is based on the one from AngularJS project([doc][angularjs-doc],
+We are using the following convention for writing git commit messages. For pull
+requests, make sure the pull request title and description follow this
+convention, as the squash-merge commit will inherit title and body from the
+pull request.
+
+This convention is based on the one from the AngularJS project ([doc][angularjs-doc],
 [commits][angularjs-git]).
 
+
 [angularjs-git]: https://github.com/angular/angular.js/commits/master
 [angularjs-doc]: https://docs.google.com/document/d/1QrDFcIiPjSLDn3EL15IJygNPiHORgU1_OOAqWjiDU5Y/edit#
 

doc/dev/ffi.md

@@ -111,6 +111,15 @@ if (lean_io_result_is_ok(res)) {
 lean_io_mark_end_initialization();
 ```
 
+In addition, any other thread not spawned by the Lean runtime itself must be initialized for Lean use by calling
+```c
+void lean_initialize_thread();
+```
+and should be finalized in order to free all thread-local resources by calling
+```c
+void lean_finalize_thread();
+```
+
 ## `@[extern]` in the Interpreter
 
 The interpreter can run Lean declarations for which symbols are available in loaded shared libraries, which includes `@[extern]` declarations.
@@ -121,4 +130,4 @@ Thus to e.g. run `#eval` on such a declaration, you need to
 Note that it is not sufficient to load the foreign library containing the external symbol because the interpreter depends on code that is emitted for each `@[extern]` declaration.
 Thus it is not possible to interpret an `@[extern]` declaration in the same file.
 
-See `tests/compiler/foreign` for an example.
+See [`tests/compiler/foreign`](https://github.com/leanprover/lean4/tree/master/tests/compiler/foreign/) for an example.

doc/dev/index.md

@@ -1,6 +1,6 @@
 # Development Workflow
 
-If you want to make changes to Lean itself, start by [building Lean](../make/index.html) from a clean checkout to make sure that everything is set up correctly.
+If you want to make changes to Lean itself, start by [building Lean](../make/index.md) from a clean checkout to make sure that everything is set up correctly.
 After that, read on below to find out how to set up your editor for changing the Lean source code, followed by further sections of the development manual where applicable such as on the [test suite](testing.md) and [commit convention](commit_convention.md).
 
 If you are planning to make any changes that may affect the compilation of Lean itself, e.g. changes to the parser, elaborator, or compiler, you should first read about the [bootstrapping pipeline](bootstrap.md).
@@ -30,20 +30,14 @@ powershell -f elan-init.ps1 --default-toolchain none
 del elan-init.ps1
 ```
 
-You can use `elan toolchain link` to give a specific stage build
-directory a reference name, then use `elan override set` to associate
-such a name to the current directory. We usually want to use `stage0`
-for editing files in `src` and `stage1` for everything else (e.g.
-tests).
+The `lean-toolchain` files in the Lean 4 repository are set up to use the `lean4-stage0`
+toolchain for editing files in `src` and the `lean4` toolchain for editing files in `tests`.
+
+Run the following commands to make `lean4` point at `stage1` and `lean4-stage0` point at `stage0`:
 ```bash
 # in the Lean rootdir
 elan toolchain link lean4 build/release/stage1
 elan toolchain link lean4-stage0 build/release/stage0
-# make `lean` etc. point to stage1 in the rootdir and subdirs
-elan override set lean4
-cd src
-# make `lean` etc. point to stage0 anywhere inside `src`
-elan override set lean4-stage0
 ```
 
 You can also use the `+toolchain` shorthand (e.g. `lean +lean4-debug`) to switch
@@ -65,9 +59,24 @@ If you push `my-tag` to a fork in your github account `my_name`,
 you can then put `my_name/lean4:my-tag` in your `lean-toolchain` file in a project using `lake`.
 (You must use a tag name that does not start with a numeral, or contain `_`).
 
+### VS Code
+
+There is a `lean.code-workspace` file that correctly sets up VS Code with workspace roots for the stage0/stage1 setup described above as well as with other settings.
+You should always load it when working on Lean, such as by invoking
+```
+code lean.code-workspace
+```
+on the command line.
+
 ### `ccache`
 
 Lean's build process uses [`ccache`](https://ccache.dev/) if it is
 installed to speed up recompilation of the generated C code. Without
 `ccache`, you'll likely spend more time than necessary waiting on
 rebuilds - it's a good idea to make sure it's installed.
+
+### `prelude`
+Unlike most Lean projects, all submodules of the `Lean` module begin with the
+`prelude` keyword. This disables the automated import of `Init`, meaning that
+developers need to figure out their own subset of `Init` to import. This is done
+such that changing files in `Init` doesn't force a full rebuild of `Lean`.

doc/dev/release_checklist.md

@@ -0,0 +1,201 @@
+# Releasing a stable version
+
+This checklist walks you through releasing a stable version.
+See below for the checklist for release candidates.
+
+We'll use `v4.6.0` as the intended release version as a running example.
+
+- One week before the planned release, ensure that someone has written the first draft of the release blog post
+- `git checkout releases/v4.6.0`
+  (This branch should already exist, from the release candidates.)
+- `git pull`
+- In `src/CMakeLists.txt`, verify you see
+  - `set(LEAN_VERSION_MINOR 6)` (for whichever `6` is appropriate)
+  - `set(LEAN_VERSION_IS_RELEASE 1)`
+  - (both of these should already be in place from the release candidates)
+- It is possible that the `v4.6.0` section of `RELEASES.md` is out of sync between
+  `releases/v4.6.0` and `master`. This should be reconciled:
+  - Run `git diff master RELEASES.md`.
+  - You should expect to see additons on `master` in the `v4.7.0-rc1` section; ignore these.
+    (i.e. the new release notes for the upcoming release candidate).
+  - Reconcile discrepancies in the `v4.6.0` section,
+    usually via copy and paste and a commit to `releases/v4.6.0`.
+- `git tag v4.6.0`
+- `git push origin v4.6.0`
+- Now wait, while CI runs.
+  - You can monitor this at `https://github.com/leanprover/lean4/actions/workflows/ci.yml`,
+    looking for the `v4.6.0` tag.
+  - This step can take up to an hour.
+  - If you are intending to cut the next release candidate on the same day,
+    you may want to start on the release candidate checklist now.
+- Go to https://github.com/leanprover/lean4/releases and verify that the `v4.6.0` release appears.
+  - Edit the release notes on Github to select the "Set as the latest release".
+  - Copy and paste the Github release notes from the previous releases candidate for this version
+    (e.g. `v4.6.0-rc1`), and quickly sanity check.
+- Next, we will move a curated list of downstream repos to the latest stable release.
+  - For each of the repositories listed below:
+    - Make a PR to `master`/`main` changing the toolchain to `v4.6.0`.
+      The PR title should be "chore: bump toolchain to v4.6.0".
+      Since the `v4.6.0` release should be functionally identical to the last release candidate,
+      which the repository should already be on, this PR is a no-op besides changing the toolchain.
+    - Once this is merged, create the tag `v4.6.0` from `master`/`main` and push it.
+    - Merge the tag `v4.6.0` into the stable branch.
+  - We do this for the repositories:
+    - [lean4checker](https://github.com/leanprover/lean4checker)
+      - `lean4checker` uses a different version tagging scheme: use `toolchain/v4.6.0` rather than `v4.6.0`.
+    - [Std](https://github.com/leanprover-community/repl)
+    - [ProofWidgets4](https://github.com/leanprover-community/ProofWidgets4)
+      - `ProofWidgets` uses a sequential version tagging scheme, e.g. `v0.0.29`,
+        which does not refer to the toolchain being used.
+      - Make a new release in this sequence after merging the toolchain bump PR.
+      - `ProofWidgets` does not maintain a `stable` branch.
+    - [Aesop](https://github.com/leanprover-community/aesop)
+    - [Mathlib](https://github.com/leanprover-community/mathlib4)
+      - In addition to updating the `lean-toolchain` and `lakefile.lean`,
+        in `.github/workflows/build.yml.in` in the `lean4checker` section update the line
+        `git checkout toolchain/v4.6.0` to the appropriate tag,
+        and then run `.github/workflows/mk_build_yml.sh`.
+    - [REPL](https://github.com/leanprover-community/repl)
+      - Note that there are two copies of `lean-toolchain`/`lakefile.lean`:
+        in the root, and in `test/Mathlib/`.
+  - Note that there are dependencies between these packages:
+    you should update the lakefile so that you are using the `v4.6.0` tag of upstream repositories
+    (or the sequential tag for `ProofWidgets4`), and run `lake update` before committing.
+  - This means that this process is sequential; each repository must have its bump PR merged,
+    and the new tag pushed, before you can make the PR for the downstream repositories.
+    - `lean4checker` has no dependencies
+    - `Std` has no dependencies
+    - `Aesop` depends on `Std`
+    - `ProofWidgets4` depends on `Std`
+    - `Mathlib` depends on `Aesop`, `ProofWidgets4`, and `lean4checker` (and transitively on `Std`)
+    - `REPL` depends on `Mathlib` (this dependency is only for testing).
+- Merge the release announcement PR for the Lean website - it will be deployed automatically
+- Finally, make an announcement!
+  This should go in https://leanprover.zulipchat.com/#narrow/stream/113486-announce, with topic `v4.6.0`.
+  Please see previous announcements for suggested language.
+  You will want a few bullet points for main topics from the release notes.
+  Link to the blog post from the Zulip announcement.
+  Please also make sure that whoever is handling social media knows the release is out.
+
+## Optimistic(?) time estimates:
+- Initial checks and push the tag: 30 minutes.
+- Note that if `RELEASES.md` has discrepancies this could take longer!
+- Waiting for the release: 60 minutes.
+- Fixing release notes: 10 minutes.
+- Bumping toolchains in downstream repositories, up to creating the Mathlib PR: 30 minutes.
+- Waiting for Mathlib CI and bors: 120 minutes.
+- Finalizing Mathlib tags and stable branch, and updating REPL: 15 minutes.
+- Posting announcement and/or blog post: 20 minutes.
+
+# Creating a release candidate.
+
+This checklist walks you through creating the first release candidate for a version of Lean.
+
+We'll use `v4.7.0-rc1` as the intended release version in this example.
+
+- Decide which nightly release you want to turn into a release candidate.
+  We will use `nightly-2024-02-29` in this example.
+- It is essential that Std and Mathlib already have reviewed branches compatible with this nightly.
+  - Check that both Std and Mathlib's `bump/v4.7.0` branch contain `nightly-2024-02-29`
+    in their `lean-toolchain`.
+  - The steps required to reach that state are beyond the scope of this checklist, but see below!
+- Create the release branch from this nightly tag:
+    ```
+    git remote add nightly https://github.com/leanprover/lean4-nightly.git
+    git fetch nightly tag nightly-2024-02-29
+    git checkout nightly-2024-02-29
+    git checkout -b releases/v4.7.0
+    ```
+- In `RELEASES.md` remove `(development in progress)` from the `v4.7.0` section header.
+- Our current goal is to have written release notes only about major language features or breaking changes,
+  and to rely on automatically generated release notes for bugfixes and minor changes.
+  - Do not wait on `RELEASES.md` being perfect before creating the `release/v4.7.0` branch. It is essential to choose the nightly which will become the release candidate as early as possible, to avoid confusion.
+  - If there are major changes not reflected in `RELEASES.md` already, you may need to solicit help from the authors.
+  - Minor changes and bug fixes do not need to be documented in `RELEASES.md`: they will be added automatically on the Github release page.
+  - Commit your changes to `RELEASES.md`, and push.
+  - Remember that changes to `RELEASES.md` after you have branched `releases/v4.7.0` should also be cherry-picked back to `master`.
+- In `src/CMakeLists.txt`,
+  - verify that you see `set(LEAN_VERSION_MINOR 7)` (for whichever `7` is appropriate); this should already have been updated when the development cycle began.
+  - `set(LEAN_VERSION_IS_RELEASE 1)` (this should be a change; on `master` and nightly releases it is always `0`).
+  - Commit your changes to `src/CMakeLists.txt`, and push.
+- `git tag v4.7.0-rc1`
+- `git push origin v4.7.0-rc1`
+- Now wait, while CI runs.
+  - You can monitor this at `https://github.com/leanprover/lean4/actions/workflows/ci.yml`, looking for the `v4.7.0-rc1` tag.
+  - This step can take up to an hour.
+- Once the release appears at https://github.com/leanprover/lean4/releases/
+  - Edit the release notes on Github to select the "Set as a pre-release box".
+  - Copy the section of `RELEASES.md` for this version into the Github release notes.
+  - Use the title "Changes since v4.6.0 (from RELEASES.md)"
+  - Then in the "previous tag" dropdown, select `v4.6.0`, and click "Generate release notes".
+  - This will add a list of all the commits since the last stable version.
+    - Delete anything already mentioned in the hand-written release notes above.
+    - Delete "update stage0" commits, and anything with a completely inscrutable commit message.
+    - Briefly rearrange the remaining items by category (e.g. `simp`, `lake`, `bug fixes`),
+      but for minor items don't put any work in expanding on commit messages.
+  - (How we want to release notes to look is evolving: please update this section if it looks wrong!)
+- Next, we will move a curated list of downstream repos to the release candidate.
+  - This assumes that there is already a *reviewed* branch `bump/v4.7.0` on each repository
+    containing the required adaptations (or no adaptations are required).
+    The preparation of this branch is beyond the scope of this document.
+  - For each of the target repositories:
+    - Checkout the `bump/v4.7.0` branch.
+    - Verify that the `lean-toolchain` is set to the nightly from which the release candidate was created.
+    - `git merge origin/master`
+    - Change the `lean-toolchain` to `leanprover/lean4:v4.7.0-rc1`
+    - In `lakefile.lean`, change any dependencies which were using `nightly-testing` or `bump/v4.7.0` branches
+      back to `master` or `main`, and run `lake update` for those dependencies.
+    - Run `lake build` to ensure that dependencies are found (but it's okay to stop it after a moment).
+    - `git commit`
+    - `git push`
+    - Open a PR from `bump/v4.7.0` to `master`, and either merge it yourself after CI, if appropriate,
+      or notify the maintainers that it is ready to go.
+    - Once this PR has been merged, tag `master` with `v4.7.0-rc1` and push this tag.
+  - We do this for the same list of repositories as for stable releases, see above.
+    As above, there are dependencies between these, and so the process above is iterative.
+    It greatly helps if you can merge the `bump/v4.7.0` PRs yourself!
+  - For Std/Aesop/Mathlib, which maintain a `nightly-testing` branch, make sure there is a tag
+    `nightly-testing-2024-02-29` with date corresponding to the nightly used for the release
+    (create it if not), and then on the `nightly-testing` branch `git reset --hard master`, and force push.
+- Make an announcement!
+  This should go in https://leanprover.zulipchat.com/#narrow/stream/113486-announce, with topic `v4.7.0-rc1`.
+  Please see previous announcements for suggested language.
+  You will want a few bullet points for main topics from the release notes.
+  Please also make sure that whoever is handling social media knows the release is out.
+- Begin the next development cycle (i.e. for `v4.8.0`) on the Lean repository, by making a PR that:
+  - Updates `src/CMakeLists.txt` to say `set(LEAN_VERSION_MINOR 8)`
+  - Removes `(in development)` from the section heading in `RELEASES.md` for `v4.7.0`,
+    and creates a new `v4.8.0 (in development)` section heading.
+
+## Time estimates:
+Slightly longer than the corresponding steps for a stable release.
+Similar process, but more things go wrong.
+In particular, updating the downstream repositories is significantly more work
+(because we need to merge existing `bump/v4.7.0` branches, not just update a toolchain).
+
+# Preparing `bump/v4.7.0` branches
+
+While not part of the release process per se,
+this is a brief summary of the work that goes into updating Std/Aesop/Mathlib to new versions.
+
+Please read https://leanprover-community.github.io/contribute/tags_and_branches.html
+
+* Each repo has an unreviewed `nightly-testing` branch that
+  receives commits automatically from `master`, and
+  has its toolchain updated automatically for every nightly.
+  (Note: the aesop branch is not automated, and is updated on an as needed basis.)
+  As a consequence this branch is often broken.
+  A bot posts in the (private!) "Mathlib reviewers" stream on Zulip about the status of these branches.
+* We fix the breakages by committing directly to `nightly-testing`: there is no PR process.
+  * This can either be done by the person managing this process directly,
+    or by soliciting assistance from authors of files, or generally helpful people on Zulip!
+* Each repo has a `bump/v4.7.0` which accumulates reviewed changes adapting to new versions.
+* Once `nightly-testing` is working on a given nightly, say `nightly-2024-02-15`, we:
+  * Make sure `bump/v4.7.0` is up to date with `master` (by merging `master`, no PR necessary)
+  * Create from `bump/v4.7.0` a `bump/nightly-2024-02-15` branch.
+  * In that branch, `git merge --squash nightly-testing` to bring across changes from `nightly-testing`.
+  * Sanity check changes, commit, and make a PR to `bump/v4.7.0` from the `bump/nightly-2024-02-15` branch.
+  * Solicit review, merge the PR into `bump/v4,7,0`.
+* It is always okay to merge in the following directions:
+  `master` -> `bump/v4.7.0` -> `bump/nightly-2024-02-15` -> `nightly-testing`.
+  Please remember to push any merges you make to intermediate steps!

doc/dev/testing.md

@@ -5,7 +5,6 @@ After [building Lean](../make/index.md) you can run all the tests using
 cd build/release
 make test ARGS=-j4
 ```
-
 Change the 4 to the maximum number of parallel tests you want to
 allow. The best choice is the number of CPU cores on your machine as
 the tests are mostly CPU bound.  You can find the number of processors
@@ -17,6 +16,12 @@ adding the `-C stageN` argument. The default when run as above is stage 1.  The
 Lean tests will automatically use that stage's corresponding Lean
 executables
 
+Running `make test` will not pick up new test files; run
+```bash
+cmake build/release/stage1
+```
+to update the list of tests.
+
 You can also use `ctest` directly if you are in the right folder.  So
 to run stage1 tests with a 300 second timeout run this:
 
@@ -24,6 +29,9 @@ to run stage1 tests with a 300 second timeout run this:
 cd build/release/stage1
 ctest -j 4 --output-on-failure --timeout 300
 ```
+Useful `ctest` flags are `-R <name of test>` to run a single test, and
+`--rerun-failed` to run all tests that failed during the last run.
+You can also pass `ctest` flags via `make test ARGS="--rerun-failed"`.
 
 To get verbose output from ctest pass the `--verbose` command line
 option. Test output is normally suppressed and only summary
@@ -33,17 +41,17 @@ information is displayed. This option will show all test output.
 
 All these tests are included by [src/shell/CMakeLists.txt](https://github.com/leanprover/lean4/blob/master/src/shell/CMakeLists.txt):
 
-- `tests/lean`: contains tests that come equipped with a
-  .lean.expected.out file. The driver script `test_single.sh` runs
+- [`tests/lean`](https://github.com/leanprover/lean4/tree/master/tests/lean/): contains tests that come equipped with a
+  .lean.expected.out file. The driver script [`test_single.sh`](https://github.com/leanprover/lean4/tree/master/tests/lean/test_single.sh) runs
   each test and checks the actual output (*.produced.out) with the
   checked in expected output.
 
-- `tests/lean/run`: contains tests that are run through the lean
+- [`tests/lean/run`](https://github.com/leanprover/lean4/tree/master/tests/lean/run/): contains tests that are run through the lean
   command line one file at a time. These tests only look for error
   codes and do not check the expected output even though output is
   produced, it is ignored.
 
-- `tests/lean/interactive`: are designed to test server requests at a
+- [`tests/lean/interactive`](https://github.com/leanprover/lean4/tree/master/tests/lean/interactive/): are designed to test server requests at a
   given position in the input file. Each .lean file contains comments
   that indicate how to simulate a client request at that position.
   using a `--^` point to the line position. Example:
@@ -53,7 +61,7 @@ All these tests are included by [src/shell/CMakeLists.txt](https://github.com/le
     Bla.
       --^ textDocument/completion
     ```
-    In this example, the test driver `test_single.sh` will simulate an
+    In this example, the test driver [`test_single.sh`](https://github.com/leanprover/lean4/tree/master/tests/lean/interactive/test_single.sh) will simulate an
     auto-completion request at `Bla.`. The expected output is stored in
     a .lean.expected.out in the json format that is part of the
     [Language Server
@@ -70,21 +78,21 @@ All these tests are included by [src/shell/CMakeLists.txt](https://github.com/le
     --^ collectDiagnostics
     ```
 
-- `tests/lean/server`: Tests more of the Lean `--server` protocol.
+- [`tests/lean/server`](https://github.com/leanprover/lean4/tree/master/tests/lean/server/): Tests more of the Lean `--server` protocol.
   There are just a few of them, and it uses .log files containing
   JSON.
 
-- `tests/compiler`: contains tests that will run the Lean compiler and
+- [`tests/compiler`](https://github.com/leanprover/lean4/tree/master/tests/compiler/): contains tests that will run the Lean compiler and
   build an executable that is executed and the output is compared to
   the .lean.expected.out file. This test also contains a subfolder
-  `foreign` which shows how to extend Lean using C++.
+  [`foreign`](https://github.com/leanprover/lean4/tree/master/tests/compiler/foreign/) which shows how to extend Lean using C++.
 
-- `tests/lean/trust0`: tests that run Lean in a mode that Lean doesn't
+- [`tests/lean/trust0`](https://github.com/leanprover/lean4/tree/master/tests/lean/trust0): tests that run Lean in a mode that Lean doesn't
   even trust the .olean files (i.e., trust 0).
 
-- `tests/bench`: contains performance tests.
+- [`tests/bench`](https://github.com/leanprover/lean4/tree/master/tests/bench/): contains performance tests.
 
-- `tests/plugin`: tests that compiled Lean code can be loaded into
+- [`tests/plugin`](https://github.com/leanprover/lean4/tree/master/tests/plugin/): tests that compiled Lean code can be loaded into
   `lean` via the `--plugin` command line option.
 
 ## Writing Good Tests
@@ -95,7 +103,7 @@ Every test file should contain:
   and, if not 100% clear, why that is the desirable behavior
 
 At the time of writing, most tests do not follow these new guidelines yet.
-For an example of a conforming test, see `tests/lean/1971.lean`.
+For an example of a conforming test, see [`tests/lean/1971.lean`](https://github.com/leanprover/lean4/tree/master/tests/lean/1971.lean).
 
 ## Fixing Tests
 
@@ -111,7 +119,7 @@ First, we must install [meld](http://meldmerge.org/). On Ubuntu, we can do it by
 sudo apt-get install meld
 ```
 
-Now, suppose `bad_class.lean` test is broken. We can see the problem by going to `tests/lean` directory and
+Now, suppose `bad_class.lean` test is broken. We can see the problem by going to [`tests/lean`](https://github.com/leanprover/lean4/tree/master/tests/lean) directory and
 executing
 
 ```
@@ -124,8 +132,3 @@ outputs. `meld` can also be used to repair the problems.
 
 In Emacs, we can also execute `M-x lean4-diff-test-file` to check/diff the file of the current buffer.
 To mass-copy all `.produced.out` files to the respective `.expected.out` file, use `tests/lean/copy-produced`.
-When using the Nix setup, add `--keep-failed` to the `nix build` call and then call
-```sh
-tests/lean/copy-produced <build-dir>/source/tests/lean
-```
-instead where `<build-dir>` is the path printed out by `nix build`.

doc/examples/bintree.lean

@@ -277,14 +277,13 @@ theorem BinTree.find_insert (b : BinTree β) (k : Nat) (v : β)
     . by_cases' key < k
       cases h; apply ihr; assumption
 
-theorem BinTree.find_insert_of_ne (b : BinTree β) (h : k ≠ k') (v : β)
+theorem BinTree.find_insert_of_ne (b : BinTree β) (ne : k ≠ k') (v : β)
         : (b.insert k v).find? k' = b.find? k' := by
   let ⟨t, h⟩ := b; simp
   induction t with simp
   | leaf =>
-    split <;> (try simp) <;> split <;> (try simp)
-    have_eq k k'
-    contradiction
+    intros le
+    exact Nat.lt_of_le_of_ne le ne
   | node left key value right ihl ihr =>
     let .node hl hr bl br := h
     specialize ihl bl

doc/examples/palindromes.lean

@@ -82,7 +82,7 @@ theorem List.palindrome_ind (motive : List α → Prop)
     have ih := palindrome_ind motive h₁ h₂ h₃ (a₂::as').dropLast
     have : [a₁] ++ (a₂::as').dropLast ++ [(a₂::as').last (by simp)] = a₁::a₂::as' := by simp
     this ▸ h₃ _ _ _ ih
-termination_by _ as => as.length
+termination_by as.length
 
 /-!
 We use our new induction principle to prove that if `as.reverse = as`, then `Palindrome as` holds.

doc/examples/widgets.lean

@@ -15,9 +15,8 @@ sections of a Lean document. User widgets are rendered in the Lean infoview.
 To try it out, simply type in the following code and place your cursor over the `#widget` command.
 -/
 
-@[widget]
-def helloWidget : UserWidgetDefinition where
-  name := "Hello"
+@[widget_module]
+def helloWidget : Widget.Module where
   javascript := "
     import * as React from 'react';
     export default function(props) {
@@ -25,7 +24,7 @@ def helloWidget : UserWidgetDefinition where
       return React.createElement('p', {}, name + '!')
     }"
 
-#widget helloWidget .null
+#widget helloWidget
 
 /-!
 If you want to dive into a full sample right away, check out
@@ -56,7 +55,11 @@ to the React component. In our first invocation of `#widget`, we set it to `.nul
 happens when you type in:
 -/
 
-#widget helloWidget (Json.mkObj [("name", "<your name here>")])
+structure HelloWidgetProps where
+  name? : Option String := none
+  deriving Server.RpcEncodable
+
+#widget helloWidget with { name? := "<your name here>" : HelloWidgetProps }
 
 /-!
 💡 NOTE: The RPC system presented below does not depend on JavaScript. However the primary use case
@@ -132,9 +135,8 @@ on this we either display an `InteractiveCode` with the type, `mapRpcError` the
 to turn it into a readable message, or show a `Loading..` message, respectively.
 -/
 
-@[widget]
-def checkWidget : UserWidgetDefinition where
-  name := "#check as a service"
+@[widget_module]
+def checkWidget : Widget.Module where
   javascript := "
 import * as React from 'react';
 const e = React.createElement;
@@ -160,7 +162,7 @@ export default function(props) {
 Finally we can try out the widget.
 -/
 
-#widget checkWidget .null
+#widget checkWidget
 
 /-!
 ![`#check` as a service](../images/widgets_caas.png)
@@ -193,9 +195,8 @@ interact with the text editor.
 You can see the full API for this [here](https://github.com/leanprover/vscode-lean4/blob/master/lean4-infoview-api/src/infoviewApi.ts#L52)
 -/
 
-@[widget]
-def insertTextWidget : UserWidgetDefinition where
-  name := "textInserter"
+@[widget_module]
+def insertTextWidget : Widget.Module where
   javascript := "
 import * as React from 'react';
 const e = React.createElement;
@@ -213,4 +214,4 @@ export default function(props) {
 
 /-! Finally, we can try this out: -/
 
-#widget insertTextWidget .null
+#widget insertTextWidget

doc/flake.lock

@@ -69,15 +69,16 @@
     "leanInk": {
       "flake": false,
       "locked": {
-        "lastModified": 1666154782,
-        "narHash": "sha256-0ELqEca6jZT4BW/mqkDD+uYuxW5QlZUFlNwZkvugsg8=",
-        "owner": "digama0",
+        "lastModified": 1704976501,
+        "narHash": "sha256-FSBUsbX0HxakSnYRYzRBDN2YKmH9EkA0q9p7TSPEJTI=",
+        "owner": "leanprover",
         "repo": "LeanInk",
-        "rev": "12a2aec9b5f4aa84e84fb01a9af1da00d8aaff4e",
+        "rev": "51821e3c2c032c88e4b2956483899d373ec090c4",
         "type": "github"
       },
       "original": {
         "owner": "leanprover",
+        "ref": "refs/pull/57/merge",
         "repo": "LeanInk",
         "type": "github"
       }

doc/flake.nix

@@ -12,7 +12,7 @@
     flake = false;
   };
   inputs.leanInk = {
-    url = "github:leanprover/LeanInk";
+    url = "github:leanprover/LeanInk/refs/pull/57/merge";
     flake = false;
   };
 

doc/functions.md

@@ -32,8 +32,8 @@ def fact x :=
 
 #eval fact 100
 ```
-By default, Lean only accepts total functions. The `partial` keyword should be used when Lean cannot
-establish that a function always terminates.
+By default, Lean only accepts total functions.
+The `partial` keyword may be used to define a recursive function without a termination proof; `partial` functions compute in compiled programs, but are opaque in proofs and during type checking.
 ```lean
 partial def g (x : Nat) (p : Nat -> Bool) : Nat :=
   if p x then

doc/lexical_structure.md

@@ -8,7 +8,7 @@ A Lean program consists of a stream of UTF-8 tokens where each token
 is one of the following:
 
 ```
-   token: symbol | command | ident | string | char | numeral |
+   token: symbol | command | ident | string | raw_string | char | numeral |
         : decimal | doc_comment | mod_doc_comment | field_notation
 ```
 
@@ -79,15 +79,35 @@ special characters:
 [Unicode table](https://unicode-table.com/en/) so "\xA9 Copyright 2021" is "© Copyright 2021".
 - `\uHHHH` puts the character represented by the 4 digit hexadecimal into the string, so the following
 string "\u65e5\u672c" will become "日本" which means "Japan".
+- `\` followed by a newline and then any amount of whitespace is a "gap" that is equivalent to the empty string,
+useful for letting a string literal span across multiple lines. Gaps spanning multiple lines can be confusing,
+so the parser raises an error if the trailing whitespace contains any newlines.
 
 So the complete syntax is:
 
 ```
    string       : '"' string_item '"'
-   string_item  : string_char | string_escape
-   string_char  : [^\\]
-   string_escape: "\" ("\" | '"' | "'" | "n" | "t" | "x" hex_char{2} | "u" hex_char{4} )
+   string_item  : string_char | char_escape | string_gap
+   string_char  : [^"\\]
+   char_escape  : "\" ("\" | '"' | "'" | "n" | "t" | "x" hex_char{2} | "u" hex_char{4})
    hex_char     : [0-9a-fA-F]
+   string_gap   : "\" newline whitespace*
+```
+
+Raw String Literals
+===================
+
+Raw string literals are string literals without any escape character processing.
+They begin with `r##...#"` (with zero or more `#` characters) and end with `"#...##` (with the same number of `#` characters).
+The contents of a raw string literal may contain `"##..#` so long as the number of `#` characters
+is less than the number of `#` characters used to begin the raw string literal.
+
+```
+   raw_string          : raw_string_aux(0) | raw_string_aux(1) | raw_string_aux(2) | ...
+   raw_string_aux(n)   : 'r' '#'{n} '"' raw_string_item '"' '#'{n}
+   raw_string_item(n)  : raw_string_char | raw_string_quote(n)
+   raw_string_char     : [^"]
+   raw_string_quote(n) : '"' '#'{0..n-1}
 ```
 
 Char Literals
@@ -96,7 +116,9 @@ Char Literals
 Char literals are enclosed by single quotes (``'``).
 
 ```
-   char: "'" string_item "'"
+   char      : "'" char_item "'"
+   char_item : char_char | char_escape
+   char_char : [^'\\]
 ```
 
 Numeric Literals

doc/make/index.md

@@ -10,12 +10,9 @@ Platform-Specific Setup
 
 - [Linux (Ubuntu)](ubuntu.md)
 - [Windows (msys2)](msys2.md)
-- [Windows (Visual Studio)](msvc.md)
 - [Windows (WSL)](wsl.md)
 - [macOS (homebrew)](osx-10.9.md)
-- Linux/macOS/WSL via [Nix](https://nixos.org/nix/): Call `nix-shell` in the project root. That's it.
-- There is also an [**experimental** setup based purely on Nix](nix.md) that works fundamentally differently from the
-  make/CMake setup described on this page.
+- Linux/macOS/WSL via [Nix](https://nixos.org/nix/): Call `nix develop` in the project root. That's it.
 
 Generic Build Instructions
 --------------------------

doc/make/nix.md

@@ -1,110 +0,0 @@
-# Building with Nix
-
-While [Nix](https://nixos.org/nix/) can be used to quickly open a shell with all dependencies for the [standard setup](index.md) installed, the user-facing [Nix Setup](../setup.md#nix-setup) can also be used to work *on* Lean.
-
-## Setup
-
-Follow the setup in the link above; to open the Lean shell inside a Lean checkout, you can also use
-```bash
-# in the Lean root directory
-$ nix-shell -A nix
-```
-
-On top of the local and remote Nix cache, we do still rely on CCache as well to make C/C++ build steps incremental, which are atomic steps from Nix's point of view.
-To enable CCache, add the following line to the config file mentioned in the setup:
-```bash
-extra-sandbox-paths = /nix/var/cache/ccache
-```
-Then set up that directory as follows:
-```bash
-sudo mkdir -m0770 -p /nix/var/cache/ccache
-# macOS standard chown doesn't support --reference
-nix shell .#nixpkgs.coreutils -c sudo chown --reference=/nix/store /nix/var/cache/ccache
-```
-
-## Basic Build Commands
-
-From the Lean root directory inside the Lean shell:
-```bash
-nix build .#stage1  # build this stage's stdlib & executable
-nix build .#stage1.test  # run all tests
-nix run .#stage1.update-stage0  # update ./stage0 from this stage
-nix run .#stage1.update-stage0-commit  # ...and commit the results
-```
-The `stage1.` part in each command is optional:
-```bash
-nix build .#test  # run tests for stage 1
-nix build .  # build stage 1
-nix build  # ditto
-```
-
-## Build Process Description
-
-The Nix build process conceptually works the same as described in [Lean Build Pipeline](index.md#lean-build-pipeline).
-However, there are two important differences in practice apart from the standard Nix properties (hermeneutic, reproducible builds stored in a global hash-indexed store etc.):
-* Only files tracked by git (using `git add` or at least `git add --intent-to-add`) are compiled.
-This is actually a general property of Nix flakes, and has the benefit of making it basically impossible to forget to commit a file (at least in `src/`).
-* Only files reachable from `src/Lean.lean` are compiled.
-This is because modules are discovered not from a directory listing anymore but by recursively compiling all dependencies of that top module.
-
-## Editor Integration
-
-As in the standard Nix setup.
-After adding `src/` as an LSP workspace, it should automatically fall back to using stage 0 in there.
-
-Note that the UX of `{emacs,vscode}-dev` is quite different from the Make-based setup regarding the compilation of dependencies:
-there is no mutable directory incrementally filled by the build that we could point the editor at for .olean files.
-Instead, `emacs-dev` will gather the individual dependency outputs from the Nix store when checking a file -- and build them on the fly when necessary.
-However, it will only ever load changes saved to disk, not ones opened in other buffers.
-
-The absence of a mutable output directory also means that the Lean server will not automatically pick up `.ilean` metadata from newly compiled files.
-Instead, you can run `nix run .#link-ilean` to symlink the `.ilean` tree of the stdlib state at that point in time to `src/build/lib`, where the server should automatically find them.
-
-## Other Fun Stuff to Do with Nix
-
-Open Emacs with Lean set up from an arbitrary commit (without even cloning Lean beforehand... if your Nix is new enough):
-```bash
-nix run github:leanprover/lean4/7e4edeb#emacs-package
-```
-
-Open a shell with `lean` and `LEAN_PATH` set up for compiling a specific module (this is exactly what `emacs-dev` is doing internally):
-```bash
-nix develop .#mods.\"Lean.Parser.Basic\"
-# alternatively, directly pass a command to execute:
-nix develop .#stage2.mods.\"Init.Control.Basic\" -c bash -c 'lean $src -Dtrace.Elab.command=true'
-```
-
-Not sure what you just broke? Run Lean from (e.g.) the previous commit on a file:
-```bash
-nix run .\?rev=$(git rev-parse @^) scratch.lean
-```
-
-Work on two adjacent stages at the same time without the need for repeatedly updating and reverting `stage0/`:
-```bash
-# open an editor that will use only committed changes (so first commit them when changing files)
-nix run .#HEAD-as-stage1.emacs-dev&
-# open a second editor that will use those committed changes as stage 0
-# (so don't commit changes done here until you are done and ran a final `update-stage0-commit`)
-nix run .#HEAD-as-stage0.emacs-dev&
-```
-To run `nix build` on the second stage outside of the second editor, use
-```bash
-nix build .#stage0-from-input --override-input lean-stage0 .\?rev=$(git rev-parse HEAD)
-```
-This setup will inadvertently change your `flake.lock` file, which you can revert when you are done.
-
-...more surely to come...
-
-## Debugging
-
-Since Nix copies all source files before compilation, you will need to map debug symbols back to the original path using `set substitute-path` in GDB.
-For example, for a build on Linux with the Nix sandbox activated:
-```bash
-(gdb) f
-#1  0x0000000000d23a4f in lean_inc (o=0x1) at /build/source/build/include/lean/lean.h:562
-562	/build/source/build/include/lean/lean.h: No such file or directory.
-(gdb) set substitute-path /build/source/build src
-(gdb) f
-#1  0x0000000000d23a4f in lean_inc (o=0x1) at /build/source/build/include/lean/lean.h:562
-562	static inline void lean_inc(lean_object * o) { if (!lean_is_scalar(o)) lean_inc_ref(o); }
-```

doc/metaprogramming-arith.md

@@ -60,7 +60,7 @@ While parsing `a * (b + c)`, `(b + c)` is assigned a precedence `60` by the addi
 the right argument to have precedence **at least** 71. Thus, this parse is invalid. In contrast, `(a * b) + c` assigns
 a precedence of `70` to `(a * b)`. This is compatible with addition which expects the left argument to have precedence
 **at least `60` ** (`70` is greater than `60`). Thus, the string `a * b + c` is parsed as `(a * b) + c`.
-For more details, please look at the [Lean manual on syntax extensions](../syntax.md#notations-and-precedence).
+For more details, please look at the [Lean manual on syntax extensions](./notation.md#notations-and-precedence).
 
 To go from strings into `Arith`, we define a macro to
 translate the syntax category `arith` into an `Arith` inductive value that

doc/monads/except.lean

@@ -33,7 +33,7 @@ convert the pure non-monadic value `x / y` into the required `Except` object.  S
 
 Now this return typing would get tedious if you had to include it everywhere that you call this
 function, however, Lean type inference can clean this up. For example, you can define a test
-function can calls the `divide` function and you don't need to say anything here about the fact that
+function that calls the `divide` function and you don't need to say anything here about the fact that
 it might throw an error, because that is inferred:
 -/
 def test := divide 5 0

doc/quickstart.md

@@ -1,55 +1,18 @@
 # Quickstart
 
-These instructions will walk you through setting up Lean using the "basic" setup and VS Code as the editor.
-See [Setup](./setup.md) for other ways, supported platforms, and more details on setting up Lean.
-
-See quick [walkthrough demo video](https://www.youtube.com/watch?v=yZo6k48L0VY).
+These instructions will walk you through setting up Lean 4 together with VS Code as an editor for Lean 4.
+See [Setup](./setup.md) for supported platforms and other ways to set up Lean 4.
 
 1. Install [VS Code](https://code.visualstudio.com/).
 
-1. Launch VS Code and install the `lean4` extension.
+1. Launch VS Code and install the `lean4` extension by clicking on the "Extensions" sidebar entry and searching for "lean4".
 
     ![installing the vscode-lean4 extension](images/code-ext.png)
 
-1. Create a new file using "File > New Text File" (`Ctrl+N`). Click the `Select a language` prompt, type in `lean4`, and hit ENTER.  You should see the following popup:
-    ![elan](images/install_elan.png)
+1. Open the Lean 4 setup guide by creating a new text file using "File > New Text File" (`Ctrl+N`), clicking on the ∀-symbol in the top right and selecting "Documentation… > Setup: Show Setup Guide".
 
-    Click the "Install Lean using Elan" button. You should see some progress output like this:
+    ![show setup guide](images/show-setup-guide.png)
 
-    ```
-    info: syncing channel updates for 'stable'
-    info: latest update on stable, lean version v4.0.0
-    info: downloading component 'lean'
-    ```
-    If there is no popup, you probably have Elan installed already.
-    You may want to make sure that your default toolchain is Lean 4 in this case by running `elan default leanprover/lean4:stable` and reopen the file, as the next step will fail otherwise.
+1. Follow the Lean 4 setup guide. It will walk you through learning resources for Lean 4, teach you how to set up Lean's dependencies on your platform, install Lean 4 for you at the click of a button and help you set up your first project.
 
-1. While it is installing, you can paste the following Lean program into the new file:
-
-    ```lean
-    #eval Lean.versionString
-    ```
-
-    When the installation has finished, the Lean Language Server should start automatically and you should get syntax-highlighting and a "Lean Infoview" popping up on the right.  You will see the output of the `#eval` statement when
-    you place your cursor at the end of the statement.
-
-    ![successful setup](images/code-success.png)
-
-You are set up!
-
-## Create a Lean Project
-
-*If your goal is to contribute to [mathlib4](https://github.com/leanprover-community/mathlib4) or use it as a dependency, please see its readme for specific instructions on how to do that.*
-
-You can now create a Lean project in a new folder. Run `lake init foo` from "View > Terminal" to create a package, followed by `lake build` to get an executable version of your Lean program.
-On Linux/macOS, you first have to follow the instructions printed by the Lean installation or log out and in again for the Lean executables to be available in you terminal.
-
-Note: Packages **have** to be opened using "File > Open Folder..." for imports to work.
-Saved changes are visible in other files after running "Lean 4: Refresh File Dependencies" (`Ctrl+Shift+X`).
-
-## Troubleshooting
-
-**The InfoView says "Waiting for Lean server to start..." forever.**
-
-Check that the VS Code Terminal is not showing some installation errors from `elan`.
-If that doesn't work, try also running the VS Code command `Developer: Reload Window`.
+    ![setup guide](images/setup_guide.png)

doc/setup.md

@@ -2,7 +2,7 @@
 
 ### Tier 1
 
-Platforms built & tested by our CI, available as nightly releases via elan (see below)
+Platforms built & tested by our CI, available as binary releases via elan (see below)
 
 * x86-64 Linux with glibc 2.27+
 * x86-64 macOS 10.15+
@@ -10,13 +10,15 @@ Platforms built & tested by our CI, available as nightly releases via elan (see
 
 ### Tier 2
 
-Platforms cross-compiled but not tested by our CI, available as nightly releases
+Platforms cross-compiled but not tested by our CI, available as binary releases
 
 Releases may be silently broken due to the lack of automated testing.
 Issue reports and fixes are welcome.
 
 * aarch64 Linux with glibc 2.27+
 * aarch64 (Apple Silicon) macOS
+* x86 (32-bit) Linux
+* Emscripten Web Assembly
 
 <!--
 ### Tier 3
@@ -48,10 +50,10 @@ Foo.lean       # main file, import via `import Foo`
 Foo/
   A.lean       # further files, import via e.g. `import Foo.A`
   A/...        # further nesting
-build/         # `lake` build output directory
+.lake/         # `lake` build output directory
 ```
 
-After running `lake build` you will see a binary named `./build/bin/foo` and when you run it you should see the output:
+After running `lake build` you will see a binary named `./.lake/build/bin/foo` and when you run it you should see the output:
 ```
 Hello, world!
 ```

doc/setup/nix.md

@@ -1,71 +0,0 @@
-# Nix Setup
-
-An alternative setup based on Nix provides a perfectly reproducible development environment for your project from the Lean version down to the editor and Lean extension.
-However, it is still experimental and subject to change; in particular, it is heavily based on an unreleased version of Nix enabling [Nix Flakes](https://www.tweag.io/blog/2020-05-25-flakes/). The setup has been tested on NixOS, other Linux distributions, and macOS.
-
-After installing (any version of) Nix (<https://nixos.org/download.html>), you can easily open a shell with the particular pre-release version of Nix needed by and tested with our setup (called the "Lean shell" from here on):
-```bash
-$ nix-shell https://github.com/leanprover/lean4/archive/master.tar.gz -A nix
-```
-While this shell is sufficient for executing the steps below, it is recommended to also set the following options in `/etc/nix/nix.conf` (`nix.extraOptions` in NixOS):
-```
-max-jobs = auto  # Allow building multiple derivations in parallel
-keep-outputs = true  # Do not garbage-collect build time-only dependencies (e.g. clang)
-# Allow fetching build results from the Lean Cachix cache
-trusted-substituters = https://lean4.cachix.org/
-trusted-public-keys = cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY= lean4.cachix.org-1:mawtxSxcaiWE24xCXXgh3qnvlTkyU7evRRnGeAhD4Wk=
-```
-On a multi-user installation of Nix (the default), you need to restart the Nix daemon afterwards:
-```bash
-sudo pkill nix-daemon
-```
-
-The [Cachix](https://cachix.org/) integration will magically beam any build steps already executed by the CI right onto your machine when calling Nix commands in the shell opened above.
-It can be set up analogously as a cache for your own project.
-
-Note: Your system Nix might print warnings about not knowing some of the settings used by the Lean shell Nix, which can be ignored.
-
-## Basic Commands
-
-From a Lean shell, run
-```bash
-$ nix flake new mypkg -t github:leanprover/lean4
-```
-to create a new Lean package in directory `mypkg` using the latest commit of Lean 4.
-Such packages follow the same directory layout as described in the standard setup, except for a `lakefile.lean` replaced by a `flake.nix` file set up so you can run Nix commands on it, for example:
-```bash
-$ nix build  # build package and all dependencies
-$ nix build .#executable  # compile `main` definition into executable (after you've added one)
-$ nix run .#emacs-dev  # open a pinned version of Emacs with lean4-mode fully set up
-$ nix run .#emacs-dev MyPackage.lean  # arguments can be passed as well, e.g. the file to open
-$ nix run .#vscode-dev MyPackage.lean  # ditto, using VS Code
-```
-Note that if you rename `MyPackage.lean`, you also have to adjust the `name` attribute in `flake.nix` accordingly.
-Also note that if you turn the package into a Git repository, only tracked files will be visible to Nix.
-
-As in the standard setup, changes need to be saved to be visible in other files, which have then to be invalidated via an editor command.
-
-If you don't want to or cannot start the pinned editor from Nix, e.g. because you're running Lean inside WSL/a container/on a different machine, you can manually point your editor at the `lean` wrapper script the commands above use internally:
-```bash
-$ nix build .#lean-dev -o result-lean-dev
-```
-The resulting `./result-lean-dev/bin/lean` script essentially runs `nix run .#lean` in the current project's root directory when you open a Lean file or use the "refresh dependencies" command such that the correct Lean version for that project is executed.
-This includes selecting the correct stage of Lean (which it will compile on the fly, though without progress output) if you are [working on Lean itself](./make/nix.md#editor-integration).
-
-Package dependencies can be added as further input flakes and passed to the `deps` list of `buildLeanPackage`. Example: <https://github.com/Kha/testpkg2/blob/master/flake.nix#L5>
-
-For hacking, it can be useful to temporarily override an input with a local checkout/different version of a dependency:
-```bash
-$ nix build --override-input somedep path/to/somedep
-```
-
-On a build error, Nix will show the last 10 lines of the output by default. You can pass `-L` to `nix build` to show all lines, or pass the shown `*.drv` path to `nix log` to show the full log after the fact.
-
-Keeping all outputs ever built on a machine alive can accumulate to quite impressive amounts of disk space, so you might want to trigger the Nix GC when `/nix/store/` has grown too large:
-```bash
-nix-collect-garbage
-```
-This will remove everything not reachable from "GC roots" such as the `./result` symlink created by `nix build`.
-
-Note that the package information in `flake.nix` is currently completely independent from `lakefile.lean` used in the standard setup.
-Unifying the two formats is TBD.

doc/syntax_highlight_in_latex.md

@@ -67,6 +67,9 @@ theorem funext {f₁ f₂ : ∀ (x : α), β x} (h : ∀ x, f₁ x = f₂ x) : f
 \end{document}
 ```
 
+If your version of `minted` is v2.7 or newer, but before v3.0,
+you will additionally need to follow the workaround described in https://github.com/gpoore/minted/issues/360.
+
 You can then compile `test.tex` by executing the following command:
 
 ```bash

doc/tour.md

@@ -15,7 +15,7 @@ The most fundamental pieces of any Lean program are functions organized into nam
 [Functions](./functions.md) perform work on inputs to produce outputs,
 and they are organized under [namespaces](./namespaces.md),
 which are the primary way you group things in Lean.
-They are defined using the [`def`](./definitions.md) command,
+They are defined using the `def` command,
 which give the function a name and define its arguments.
 
 ```lean

doc/typeclass.md

@@ -99,11 +99,11 @@ Let us start with the first step of the program above, declaring an appropriate
 
 ```lean
 # namespace Ex
-class Inhabited (a : Type u) where
+class Inhabited (a : Sort u) where
   default : a
 
 #check @Inhabited.default
--- Inhabited.default : {a : Type u} → [self : Inhabited a] → a
+-- Inhabited.default : {a : Sort u} → [self : Inhabited a] → a
 # end Ex
 ```
 Note `Inhabited.default` doesn't have any explicit argument.
@@ -114,7 +114,7 @@ Now we populate the class with some instances:
 
 ```lean
 # namespace Ex
-# class Inhabited (a : Type _) where
+# class Inhabited (a : Sort _) where
 #  default : a
 instance : Inhabited Bool where
   default := true
@@ -138,7 +138,7 @@ instance : Inhabited Prop where
 You can use the command `export` to create the alias `default` for `Inhabited.default`
 ```lean
 # namespace Ex
-# class Inhabited (a : Type _) where
+# class Inhabited (a : Sort _) where
 #  default : a
 # instance : Inhabited Bool where
 #  default := true
@@ -174,7 +174,7 @@ instance [Inhabited a] [Inhabited b] : Inhabited (a × b) where
 With this added to the earlier instance declarations, type class instance can infer, for example, a default element of ``Nat × Bool``:
 ```lean
 # namespace Ex
-# class Inhabited (a : Type u) where
+# class Inhabited (a : Sort u) where
 #  default : a
 # instance : Inhabited Bool where
 #  default := true
@@ -191,8 +191,14 @@ instance [Inhabited a] [Inhabited b] : Inhabited (a × b) where
 ```
 Similarly, we can inhabit type function with suitable constant functions:
 ```lean
+# namespace Ex
+# class Inhabited (a : Sort u) where
+#  default : a
+# opaque default [Inhabited a] : a :=
+#  Inhabited.default
 instance [Inhabited b] : Inhabited (a -> b) where
   default := fun _ => default
+# end Ex
 ```
 As an exercise, try defining default instances for other types, such as `List` and `Sum` types.
 

doc/whatIsLean.md

@@ -37,6 +37,6 @@ Lean has numerous features, including:
 - [Extensible syntax](./syntax.md)
 - Hygienic macros
 - [Dependent types](https://lean-lang.org/theorem_proving_in_lean4/dependent_type_theory.html)
-- [Metaprogramming](./metaprogramming.md)
+- [Metaprogramming](./macro_overview.md)
 - Multithreading
 - Verification: you can prove properties of your functions using Lean itself

flake.lock

@@ -83,6 +83,23 @@
         "type": "github"
       }
     },
+    "nixpkgs-old": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1581379743,
+        "narHash": "sha256-i1XCn9rKuLjvCdu2UeXKzGLF6IuQePQKFt4hEKRU5oc=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "34c7eb7545d155cc5b6f499b23a7cb1c96ab4d59",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-19.03",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
     "nixpkgs-regression": {
       "locked": {
         "lastModified": 1643052045,
@@ -120,7 +137,8 @@
         "flake-utils": "flake-utils",
         "lean4-mode": "lean4-mode",
         "nix": "nix",
-        "nixpkgs": "nixpkgs_2"
+        "nixpkgs": "nixpkgs_2",
+        "nixpkgs-old": "nixpkgs-old"
       }
     }
   },

flake.nix

@@ -2,6 +2,9 @@
   description = "Lean interactive theorem prover";
 
   inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+  # old nixpkgs used for portable release with older glibc (2.27)
+  inputs.nixpkgs-old.url = "github:NixOS/nixpkgs/nixos-19.03";
+  inputs.nixpkgs-old.flake = false;
   inputs.flake-utils.url = "github:numtide/flake-utils";
   inputs.nix.url = "github:NixOS/nix";
   inputs.lean4-mode = {
@@ -17,14 +20,41 @@
   #  inputs.lean4-mode.follows = "lean4-mode";
   #};
 
-  outputs = { self, nixpkgs, flake-utils, nix, lean4-mode, ... }@inputs: flake-utils.lib.eachDefaultSystem (system:
+  outputs = { self, nixpkgs, nixpkgs-old, flake-utils, nix, lean4-mode, ... }@inputs: flake-utils.lib.eachDefaultSystem (system:
     let
       pkgs = import nixpkgs {
         inherit system;
         # for `vscode-with-extensions`
         config.allowUnfree = true;
       };
+      # An old nixpkgs for creating releases with an old glibc
+      pkgsDist-old = import nixpkgs-old { inherit system; };
+      # An old nixpkgs for creating releases with an old glibc
+      pkgsDist-old-aarch = import nixpkgs-old { localSystem.config = "aarch64-unknown-linux-gnu"; };
+
       lean-packages = pkgs.callPackage (./nix/packages.nix) { src = ./.; inherit nix lean4-mode; };
+
+      devShellWithDist = pkgsDist: pkgs.mkShell.override {
+	  stdenv = pkgs.overrideCC pkgs.stdenv lean-packages.llvmPackages.clang;
+	} ({
+	  buildInputs = with pkgs; [
+	    cmake gmp ccache
+	    lean-packages.llvmPackages.llvm  # llvm-symbolizer for asan/lsan
+	    # TODO: only add when proven to not affect the flakification
+	    #pkgs.python3
+	  ];
+	  # https://github.com/NixOS/nixpkgs/issues/60919
+	  hardeningDisable = [ "all" ];
+	  # more convenient `ctest` output
+	  CTEST_OUTPUT_ON_FAILURE = 1;
+	} // pkgs.lib.optionalAttrs pkgs.stdenv.isLinux {
+	  GMP = pkgsDist.gmp.override { withStatic = true; };
+	  GLIBC = pkgsDist.glibc;
+	  GLIBC_DEV = pkgsDist.glibc.dev;
+	  GCC_LIB = pkgsDist.gcc.cc.lib;
+	  ZLIB = pkgsDist.zlib;
+	  GDB = pkgsDist.gdb;
+	});
     in {
       packages = lean-packages // rec {
         debug = lean-packages.override { debug = true; };
@@ -49,7 +79,10 @@
       };
       defaultPackage = lean-packages.lean-all;
 
-      inherit (lean-packages) devShell;
+      # The default development shell for working on lean itself
+      devShells.default = devShellWithDist pkgs;
+      devShells.oldGlibc = devShellWithDist pkgsDist-old;
+      devShells.oldGlibcAArch = devShellWithDist pkgsDist-old-aarch;
 
       checks.lean = lean-packages.test;
     }) // rec {

lean-toolchain

@@ -0,0 +1 @@
+lean4

lean.code-workspace

@@ -0,0 +1,57 @@
+{
+	"folders": [
+		{
+			"path": "."
+		},
+		{
+			"path": "src"
+		},
+		{
+			"path": "tests"
+		}
+	],
+	"settings": {
+		"files.insertFinalNewline": true,
+		"files.trimTrailingWhitespace": true,
+		"cmake.buildDirectory": "${workspaceFolder}/build/release",
+		"cmake.generator": "Unix Makefiles",
+		"[markdown]": {
+			"rewrap.wrappingColumn": 70
+		},
+		"[lean4]": {
+			"editor.rulers": [
+				100
+			]
+		}
+	},
+	"tasks": {
+		"version": "2.0.0",
+		"tasks": [
+			{
+				"label": "build",
+				"type": "shell",
+				"command": "make -C build/release -j$(nproc 2>/dev/null || sysctl -n hw.logicalcpu 2>/dev/null || echo 4)",
+				"problemMatcher": [],
+				"group": {
+					"kind": "build",
+					"isDefault": true
+				}
+			},
+			{
+				"label": "test",
+				"type": "shell",
+				"command": "NPROC=$(nproc 2>/dev/null || sysctl -n hw.logicalcpu 2>/dev/null || echo 4); CTEST_OUTPUT_ON_FAILURE=1 make -C build/release test -j$NPROC ARGS=\"-j$NPROC\"",
+				"problemMatcher": [],
+				"group": {
+					"kind": "test",
+					"isDefault": true
+				}
+			}
+		]
+	},
+	"extensions": {
+		"recommendations": [
+			"leanprover.lean4"
+		]
+	}
+}

nix/bootstrap.nix

@@ -65,12 +65,7 @@ rec {
     installPhase = ''
       mkdir -p $out/bin $out/lib/lean
       mv bin/lean $out/bin/
-      mv lib/lean/libleanshared.* $out/lib/lean
-   '' + lib.optionalString stdenv.isDarwin ''
-      for lib in $(otool -L $out/bin/lean | tail -n +2 | cut -d' ' -f1); do
-        if [[ "$lib" == *lean* ]]; then install_name_tool -change "$lib" "$out/lib/lean/$(basename $lib)" $out/bin/lean; fi
-      done
-      otool -L $out/bin/lean
+      mv lib/lean/*.{so,dylib} $out/lib/lean
     '';
     meta.mainProgram = "lean";
   });
@@ -83,13 +78,13 @@ rec {
         # use same stage for retrieving dependencies
         lean-leanDeps = stage0;
         lean-final = self;
-        leanFlags = [ "-DwarningAsError=true" ];
       } ({
         src = src + "/src";
         roots = [ { mod = args.name; glob = "andSubmodules"; } ];
         fullSrc = src;
         srcPath = "$PWD/src:$PWD/src/lake";
         inherit debug;
+        leanFlags = [ "-DwarningAsError=true" ];
       } // args);
       Init' = build { name = "Init"; deps = []; };
       Lean' = build { name = "Lean"; deps = [ Init' ]; };
@@ -120,29 +115,35 @@ rec {
       iTree = symlinkJoin { name = "ileans"; paths = map (l: l.iTree) stdlib; };
       Leanc = build { name = "Leanc"; src = lean-bin-tools-unwrapped.leanc_src; deps = stdlib; roots = [ "Leanc" ]; };
       stdlibLinkFlags = "-L${Init.staticLib} -L${Lean.staticLib} -L${Lake.staticLib} -L${leancpp}/lib/lean";
+      libInit_shared = runCommand "libInit_shared" { buildInputs = [ stdenv.cc ]; libName = "libInit_shared${stdenv.hostPlatform.extensions.sharedLibrary}"; } ''
+        mkdir $out
+        LEAN_CC=${stdenv.cc}/bin/cc ${lean-bin-tools-unwrapped}/bin/leanc -shared -Wl,-Bsymbolic \
+          -Wl,--whole-archive -lInit ${leancpp}/lib/libleanrt_initial-exec.a -Wl,--no-whole-archive -lstdc++ -lm ${stdlibLinkFlags} \
+          $(${llvmPackages.libllvm.dev}/bin/llvm-config --ldflags --libs) \
+          -o $out/$libName
+      '';
       leanshared = runCommand "leanshared" { buildInputs = [ stdenv.cc ]; libName = "libleanshared${stdenv.hostPlatform.extensions.sharedLibrary}"; } ''
         mkdir $out
-        LEAN_CC=${stdenv.cc}/bin/cc ${lean-bin-tools-unwrapped}/bin/leanc -shared ${lib.optionalString stdenv.isLinux "-Wl,-Bsymbolic"} \
-          ${if stdenv.isDarwin then "-Wl,-force_load,${Init.staticLib}/libInit.a -Wl,-force_load,${Lean.staticLib}/libLean.a -Wl,-force_load,${leancpp}/lib/lean/libleancpp.a ${leancpp}/lib/libleanrt_initial-exec.a -lc++"
-            else "-Wl,--whole-archive -lInit -lLean -lleancpp ${leancpp}/lib/libleanrt_initial-exec.a -Wl,--no-whole-archive -lstdc++"} -lm ${stdlibLinkFlags} \
+        LEAN_CC=${stdenv.cc}/bin/cc ${lean-bin-tools-unwrapped}/bin/leanc -shared -Wl,-Bsymbolic \
+          ${libInit_shared}/* -Wl,--whole-archive -lLean -lleancpp -Wl,--no-whole-archive -lstdc++ -lm ${stdlibLinkFlags} \
           $(${llvmPackages.libllvm.dev}/bin/llvm-config --ldflags --libs) \
           -o $out/$libName
       '';
       mods = foldl' (mods: pkg: mods // pkg.mods) {} stdlib;
       print-paths = Lean.makePrintPathsFor [] mods;
       leanc = writeShellScriptBin "leanc" ''
-        LEAN_CC=${stdenv.cc}/bin/cc ${Leanc.executable}/bin/leanc -I${lean-bin-tools-unwrapped}/include ${stdlibLinkFlags} -L${leanshared} "$@"
+        LEAN_CC=${stdenv.cc}/bin/cc ${Leanc.executable}/bin/leanc -I${lean-bin-tools-unwrapped}/include ${stdlibLinkFlags} -L${libInit_shared} -L${leanshared} "$@"
       '';
       lean = runCommand "lean" { buildInputs = lib.optional stdenv.isDarwin darwin.cctools; } ''
         mkdir -p $out/bin
-        ${leanc}/bin/leanc ${leancpp}/lib/lean.cpp.o ${leanshared}/* -o $out/bin/lean
+        ${leanc}/bin/leanc ${leancpp}/lib/lean.cpp.o ${libInit_shared}/* ${leanshared}/* -o $out/bin/lean
       '';
       # derivation following the directory layout of the "basic" setup, mostly useful for running tests
       lean-all = stdenv.mkDerivation {
         name = "lean-${desc}";
         buildCommand = ''
           mkdir -p $out/bin $out/lib/lean
-          ln -sf ${leancpp}/lib/lean/* ${lib.concatMapStringsSep " " (l: "${l.modRoot}/* ${l.staticLib}/*") (lib.reverseList stdlib)} ${leanshared}/* $out/lib/lean/
+          ln -sf ${leancpp}/lib/lean/* ${lib.concatMapStringsSep " " (l: "${l.modRoot}/* ${l.staticLib}/*") (lib.reverseList stdlib)} ${libInit_shared}/* ${leanshared}/* $out/lib/lean/
           # put everything in a single final derivation so `IO.appDir` references work
           cp ${lean}/bin/lean ${leanc}/bin/leanc ${Lake-Main.executable}/bin/lake $out/bin
           # NOTE: `lndir` will not override existing `bin/leanc`

nix/buildLeanPackage.nix

@@ -10,7 +10,7 @@ lib.makeOverridable (
   staticLibDeps ? [],
   # Whether to wrap static library inputs in a -Wl,--start-group [...] -Wl,--end-group to ensure dependencies are resolved.
   groupStaticLibs ? false,
-  # Shared library dependencies included at interpretation with --load-dynlib and linked to. Each derivation `shared` should contain a 
+  # Shared library dependencies included at interpretation with --load-dynlib and linked to. Each derivation `shared` should contain a
   # shared library at the path `${shared}/${shared.libName or shared.name}` and a name to link to like `-l${shared.linkName or shared.name}`.
   # These libs are also linked to in packages that depend on this one.
   nativeSharedLibs ? [],
@@ -88,9 +88,9 @@ with builtins; let
   allNativeSharedLibs =
     lib.unique (lib.flatten (nativeSharedLibs ++ (map (dep: dep.allNativeSharedLibs or []) allExternalDeps)));
 
-  # A flattened list of all static library dependencies: this and every dep module's explicitly provided `staticLibDeps`, 
+  # A flattened list of all static library dependencies: this and every dep module's explicitly provided `staticLibDeps`,
   # plus every dep module itself: `dep.staticLib`
-  allStaticLibDeps = 
+  allStaticLibDeps =
     lib.unique (lib.flatten (staticLibDeps ++ (map (dep: [dep.staticLib] ++ dep.staticLibDeps or []) allExternalDeps)));
 
   pathOfSharedLib = dep: dep.libPath or "${dep}/${dep.libName or dep.name}";
@@ -176,7 +176,7 @@ with builtins; let
       # make local "copy" so `drv`'s Nix store path doesn't end up in ccache's hash
       ln -s ${drv.c}/${drv.cPath} src.c
       # on the other hand, a debug build is pretty fast anyway, so preserve the path for gdb
-      leanc -c -o $out/$oPath $leancFlags -fPIC ${if debug then "${drv.c}/${drv.cPath} -g" else "src.c -O3 -DNDEBUG"}
+      leanc -c -o $out/$oPath $leancFlags -fPIC ${if debug then "${drv.c}/${drv.cPath} -g" else "src.c -O3 -DNDEBUG -DLEAN_EXPORTING"}
     '';
   };
   mkMod = mod: deps:
@@ -249,7 +249,7 @@ in rec {
     ${if stdenv.isDarwin then "-Wl,-force_load,${staticLib}/lib${libName}.a" else "-Wl,--whole-archive ${staticLib}/lib${libName}.a -Wl,--no-whole-archive"} \
     ${lib.concatStringsSep " " (map (d: "${d.sharedLib}/*") deps)}'';
   executable = lib.makeOverridable ({ withSharedStdlib ? true }: let
-      objPaths = map (drv: "${drv}/${drv.oPath}") (attrValues objects) ++ lib.optional withSharedStdlib "${lean-final.leanshared}/*";
+      objPaths = map (drv: "${drv}/${drv.oPath}") (attrValues objects) ++ lib.optional withSharedStdlib "${lean-final.libInit_shared}/* ${lean-final.leanshared}/*";
     in runCommand executableName { buildInputs = [ stdenv.cc leanc ]; } ''
       mkdir -p $out/bin
       leanc ${staticLibLinkWrapper (lib.concatStringsSep " " (objPaths ++ map (d: "${d}/*.a") allStaticLibDeps))} \

nix/lake-dev.in

@@ -10,7 +10,7 @@ function pebkac() {
 [[ $# -gt 0 ]] || pebkac
 case $1 in
     --version)
-        # minimum version for `lake server` with fallback
+        # minimum version for `lake serve` with fallback
         echo 3.1.0
         ;;
     print-paths)

script/apply.lean

@@ -1,3 +1,8 @@
+/-
+Copyright (c) 2022 Sebastian Ullrich. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Sebastian Ullrich
+-/
 import Lean.Runtime
 
 abbrev M := ReaderT IO.FS.Stream IO
@@ -16,7 +21,7 @@ def mkTypedefFn (i : Nat) : M Unit := do
   emit s!"typedef obj* (*fn{i})({args}); // NOLINT\n"
   emit s!"#define FN{i}(f) reinterpret_cast<fn{i}>(lean_closure_fun(f))\n"
 
-def genSeq (n : Nat) (f : Nat → String) (sep := ", ") : String := 
+def genSeq (n : Nat) (f : Nat → String) (sep := ", ") : String :=
   List.range n |>.map f |>.intersperse sep |> .join
 
 -- make string: "obj* a1, obj* a2, ..., obj* an"

script/prepare-llvm-linux.sh

@@ -25,6 +25,8 @@ cp -L llvm/bin/llvm-ar stage1/bin/
 # dependencies of the above
 $CP llvm/lib/lib{clang-cpp,LLVM}*.so* stage1/lib/
 $CP $ZLIB/lib/libz.so* stage1/lib/
+# general clang++ dependency, breaks cross-library C++ exceptions if linked statically
+$CP $GCC_LIB/lib/libgcc_s.so* stage1/lib/
 # bundle libatomic (referenced by LLVM >= 15, and required by the lean executable to run)
 $CP $GCC_LIB/lib/libatomic.so* stage1/lib/
 
@@ -60,7 +62,7 @@ fi
 # use `-nostdinc` to make sure headers are not visible by default (in particular, not to `#include_next` in the clang headers),
 # but do not change sysroot so users can still link against system libs
 echo -n " -DLEANC_INTERNAL_FLAGS='-nostdinc -isystem ROOT/include/clang' -DLEANC_CC=ROOT/bin/clang"
-echo -n " -DLEANC_INTERNAL_LINKER_FLAGS='-L ROOT/lib -L ROOT/lib/glibc ROOT/lib/glibc/libc_nonshared.a -Wl,--as-needed -static-libgcc -Wl,-Bstatic -lgmp -lunwind -Wl,-Bdynamic -Wl,--no-as-needed -fuse-ld=lld'"
+echo -n " -DLEANC_INTERNAL_LINKER_FLAGS='-L ROOT/lib -L ROOT/lib/glibc ROOT/lib/glibc/libc_nonshared.a -Wl,--as-needed -Wl,-Bstatic -lgmp -lunwind -Wl,-Bdynamic -Wl,--no-as-needed -fuse-ld=lld'"
 # when not using the above flags, link GMP dynamically/as usual
 echo -n " -DLEAN_EXTRA_LINKER_FLAGS='-Wl,--as-needed -lgmp -Wl,--no-as-needed'"
 # do not set `LEAN_CC` for tests

shell.nix

@@ -1,27 +0,0 @@
-let
-  flake = (import ./default.nix);
-  flakePkgs = flake.packages.${builtins.currentSystem};
-in { pkgs ? flakePkgs.nixpkgs, pkgsDist ? pkgs }:
-# use `shell` as default
-(attribs: attribs.shell // attribs) rec {
-  shell = pkgs.mkShell.override {
-    stdenv = pkgs.overrideCC pkgs.stdenv flakePkgs.llvmPackages.clang;
-  } (rec {
-    buildInputs = with pkgs; [
-      cmake gmp ccache
-      flakePkgs.llvmPackages.llvm  # llvm-symbolizer for asan/lsan
-    ];
-    # https://github.com/NixOS/nixpkgs/issues/60919
-    hardeningDisable = [ "all" ];
-    # more convenient `ctest` output
-    CTEST_OUTPUT_ON_FAILURE = 1;
-  } // pkgs.lib.optionalAttrs pkgs.stdenv.isLinux {
-    GMP = pkgsDist.gmp.override { withStatic = true; };
-    GLIBC = pkgsDist.glibc;
-    GLIBC_DEV = pkgsDist.glibc.dev;
-    GCC_LIB = pkgsDist.gcc.cc.lib;
-    ZLIB = pkgsDist.zlib;
-    GDB = pkgsDist.gdb;
-  });
-  nix = flake.devShell.${builtins.currentSystem};
-}

src/CMakeLists.txt

@@ -9,7 +9,7 @@ endif()
 include(ExternalProject)
 project(LEAN CXX C)
 set(LEAN_VERSION_MAJOR 4)
-set(LEAN_VERSION_MINOR 3)
+set(LEAN_VERSION_MINOR 8)
 set(LEAN_VERSION_PATCH 0)
 set(LEAN_VERSION_IS_RELEASE 0)  # This number is 1 in the release revision, and 0 otherwise.
 set(LEAN_SPECIAL_VERSION_DESC "" CACHE STRING "Additional version description like 'nightly-2018-03-11'")
@@ -18,6 +18,14 @@ if (LEAN_SPECIAL_VERSION_DESC)
   string(APPEND LEAN_VERSION_STRING "-${LEAN_SPECIAL_VERSION_DESC}")
 endif()
 
+set(LEAN_PLATFORM_TARGET "" CACHE STRING "LLVM triple of the target platform")
+if (NOT LEAN_PLATFORM_TARGET)
+  # this may fail when the compiler is not clang, but this should only happen in local builds where
+  # the value of the variable is not of immediate relevance
+  execute_process(COMMAND ${CMAKE_C_COMPILER} --print-target-triple
+    OUTPUT_VARIABLE LEAN_PLATFORM_TARGET OUTPUT_STRIP_TRAILING_WHITESPACE)
+endif()
+
 set(LEAN_EXTRA_LINKER_FLAGS "" CACHE STRING "Additional flags used by the linker")
 set(LEAN_EXTRA_CXX_FLAGS "" CACHE STRING "Additional flags used by the C++ compiler")
 set(LEAN_TEST_VARS "LEAN_CC=${CMAKE_C_COMPILER}" CACHE STRING "Additional environment variables used when running tests")
@@ -64,10 +72,10 @@ option(BSYMBOLIC "Link with -Bsymbolic to reduce call overhead in shared librari
 option(USE_GMP "USE_GMP" ON)
 
 # development-specific options
-option(CHECK_OLEAN_VERSION "Only load .olean files compiled with the current version of Lean" ON)
+option(CHECK_OLEAN_VERSION "Only load .olean files compiled with the current version of Lean" OFF)
 
 set(LEAN_EXTRA_MAKE_OPTS  ""                           CACHE STRING "extra options to lean --make")
-set(LEANC_CC              "cc"                         CACHE STRING "C compiler to use in `leanc`")
+set(LEANC_CC              ${CMAKE_C_COMPILER}          CACHE STRING "C compiler to use in `leanc`")
 
 if ("${LAZY_RC}" MATCHES "ON")
   set(LEAN_LAZY_RC "#define LEAN_LAZY_RC")
@@ -93,8 +101,9 @@ if ("${RUNTIME_STATS}" MATCHES "ON")
   string(APPEND LEAN_EXTRA_CXX_FLAGS " -D LEAN_RUNTIME_STATS")
 endif()
 
-if (NOT("${CHECK_OLEAN_VERSION}" MATCHES "ON"))
-  string(APPEND LEAN_EXTRA_CXX_FLAGS " -D LEAN_IGNORE_OLEAN_VERSION")
+if ("${CHECK_OLEAN_VERSION}" MATCHES "ON")
+  set(USE_GITHASH ON)
+  string(APPEND LEAN_EXTRA_CXX_FLAGS " -D LEAN_CHECK_OLEAN_VERSION")
 endif()
 
 if(${CMAKE_SYSTEM_NAME} MATCHES "Emscripten")
@@ -290,13 +299,12 @@ if(${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
     cmake_path(GET ZLIB_LIBRARY PARENT_PATH ZLIB_LIBRARY_PARENT_PATH)
     string(APPEND LEANSHARED_LINKER_FLAGS " -L ${ZLIB_LIBRARY_PARENT_PATH}")
   endif()
-  string(APPEND LEANC_STATIC_LINKER_FLAGS " -lleancpp -lInit -lLean -lleanrt")
+  string(APPEND TOOLCHAIN_STATIC_LINKER_FLAGS " -lleancpp -lInit -lLean -lleanrt")
 elseif(${CMAKE_SYSTEM_NAME} MATCHES "Emscripten")
-  string(APPEND LEANC_STATIC_LINKER_FLAGS " -lleancpp -lInit -lLean -lnodefs.js -lleanrt")
+  string(APPEND TOOLCHAIN_STATIC_LINKER_FLAGS " -lleancpp -lInit -lLean -lnodefs.js -lleanrt")
 else()
-  string(APPEND LEANC_STATIC_LINKER_FLAGS " -Wl,--start-group -lleancpp -lLean -Wl,--end-group -Wl,--start-group -lInit -lleanrt -Wl,--end-group")
+  string(APPEND TOOLCHAIN_STATIC_LINKER_FLAGS " -Wl,--start-group -lleancpp -lLean -Wl,--end-group -Wl,--start-group -lInit -lleanrt -Wl,--end-group")
 endif()
-string(APPEND LEANC_STATIC_LINKER_FLAGS " -lLake")
 
 set(LEAN_CXX_STDLIB "-lstdc++" CACHE STRING "C++ stdlib linker flags")
 
@@ -304,8 +312,11 @@ if(${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
   set(LEAN_CXX_STDLIB "-lc++")
 endif()
 
-string(APPEND LEANC_STATIC_LINKER_FLAGS " ${LEAN_CXX_STDLIB}")
-string(APPEND LEANSHARED_LINKER_FLAGS " ${LEAN_CXX_STDLIB}")
+string(APPEND TOOLCHAIN_STATIC_LINKER_FLAGS " ${LEAN_CXX_STDLIB}")
+string(APPEND TOOLCHAIN_SHARED_LINKER_FLAGS " ${LEAN_CXX_STDLIB}")
+
+# flags for user binaries = flags for toolchain binaries + Lake
+string(APPEND LEANC_STATIC_LINKER_FLAGS " ${TOOLCHAIN_STATIC_LINKER_FLAGS} -lLake")
 
 if (LLVM)
   string(APPEND LEANSHARED_LINKER_FLAGS " -L${LLVM_CONFIG_LIBDIR} ${LLVM_CONFIG_LDFLAGS} ${LLVM_CONFIG_LIBS} ${LLVM_CONFIG_SYSTEM_LIBS}")
@@ -333,9 +344,9 @@ endif()
 
 # get rid of unused parts of C++ stdlib
 if(${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
-  string(APPEND LEANSHARED_LINKER_FLAGS " -Wl,-dead_strip")
+  string(APPEND TOOLCHAIN_SHARED_LINKER_FLAGS " -Wl,-dead_strip")
 elseif(NOT ${CMAKE_SYSTEM_NAME} MATCHES "Emscripten")
-  string(APPEND LEANSHARED_LINKER_FLAGS " -Wl,--gc-sections")
+  string(APPEND TOOLCHAIN_SHARED_LINKER_FLAGS " -Wl,--gc-sections")
 endif()
 
 if(NOT ${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
@@ -345,26 +356,20 @@ endif()
 if(${CMAKE_SYSTEM_NAME} MATCHES "Linux")
   if(BSYMBOLIC)
     string(APPEND LEANC_SHARED_LINKER_FLAGS " -Wl,-Bsymbolic")
-    string(APPEND LEANSHARED_LINKER_FLAGS " -Wl,-Bsymbolic")
+    string(APPEND TOOLCHAIN_SHARED_LINKER_FLAGS " -Wl,-Bsymbolic")
   endif()
   string(APPEND CMAKE_CXX_FLAGS " -fPIC -ftls-model=initial-exec")
   string(APPEND LEANC_EXTRA_FLAGS " -fPIC")
-  string(APPEND LEANSHARED_LINKER_FLAGS " -Wl,-rpath=\\$$ORIGIN/..:\\$$ORIGIN")
-  string(APPEND CMAKE_EXE_LINKER_FLAGS " -lleanshared -Wl,-rpath=\\\$ORIGIN/../lib:\\\$ORIGIN/../lib/lean")
+  string(APPEND TOOLCHAIN_SHARED_LINKER_FLAGS " -Wl,-rpath=\\$$ORIGIN/..:\\$$ORIGIN")
+  string(APPEND CMAKE_EXE_LINKER_FLAGS " -Wl,-rpath=\\\$ORIGIN/../lib:\\\$ORIGIN/../lib/lean")
 elseif(${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
   string(APPEND CMAKE_CXX_FLAGS " -ftls-model=initial-exec")
+  string(APPEND INIT_SHARED_LINKER_FLAGS " -install_name @rpath/libInit_shared.dylib")
   string(APPEND LEANSHARED_LINKER_FLAGS " -install_name @rpath/libleanshared.dylib")
-  string(APPEND CMAKE_EXE_LINKER_FLAGS " -lleanshared -Wl,-rpath,@executable_path/../lib -Wl,-rpath,@executable_path/../lib/lean")
+  string(APPEND CMAKE_EXE_LINKER_FLAGS " -Wl,-rpath,@executable_path/../lib -Wl,-rpath,@executable_path/../lib/lean")
 elseif(${CMAKE_SYSTEM_NAME} MATCHES "Emscripten")
   string(APPEND CMAKE_CXX_FLAGS " -fPIC")
   string(APPEND LEANC_EXTRA_FLAGS " -fPIC")
-  # We do not use dynamic linking via leanshared for Emscripten to keep things
-  # simple. (And we are not interested in `Lake` anyway.) To use dynamic
-  # linking, we would probably have to set MAIN_MODULE=2 on `leanshared`,
-  # SIDE_MODULE=2 on `lean`, and set CMAKE_SHARED_LIBRARY_SUFFIX to ".js".
-  string(APPEND CMAKE_EXE_LINKER_FLAGS " -Wl,--whole-archive -lInit -lLean -lleancpp -lleanrt ${EMSCRIPTEN_SETTINGS} -lnodefs.js -s EXIT_RUNTIME=1 -s MAIN_MODULE=1 -s LINKABLE=1 -s EXPORT_ALL=1")
-elseif(${CMAKE_SYSTEM_NAME} MATCHES "Windows")
-  string(APPEND CMAKE_EXE_LINKER_FLAGS " -lleanshared")
 endif()
 
 if(${CMAKE_SYSTEM_NAME} MATCHES "Linux")
@@ -390,7 +395,7 @@ endif()
 # are already loaded) and probably fail unless we set up LD_LIBRARY_PATH.
 if(${CMAKE_SYSTEM_NAME} MATCHES "Windows")
   # import library created by the `leanshared` target
-  string(APPEND LEANC_SHARED_LINKER_FLAGS " -lleanshared")
+  string(APPEND LEANC_SHARED_LINKER_FLAGS " -lInit_shared -lleanshared")
 elseif("${CMAKE_SYSTEM_NAME}" MATCHES "Darwin")
   string(APPEND LEANC_SHARED_LINKER_FLAGS " -Wl,-undefined,dynamic_lookup")
 endif()
@@ -401,26 +406,17 @@ if(MULTI_THREAD AND NOT MSVC AND (NOT ("${CMAKE_SYSTEM_NAME}" MATCHES "Darwin"))
 endif()
 
 # Git HASH
-set(LEAN_PACKAGE_VERSION "NOT-FOUND")
 if(USE_GITHASH)
   include(GetGitRevisionDescription)
   get_git_head_revision(GIT_REFSPEC GIT_SHA1)
   if(${GIT_SHA1} MATCHES "GITDIR-NOTFOUND")
     message(STATUS "Failed to read git_sha1")
     set(GIT_SHA1 "")
-    if(EXISTS "${LEAN_SOURCE_DIR}/bin/package_version")
-      file(STRINGS "${LEAN_SOURCE_DIR}/bin/package_version" LEAN_PACKAGE_VERSION)
-      message(STATUS "Package version detected: ${LEAN_PACKAGE_VERSION}")
-    endif()
   else()
     message(STATUS "git commit sha1: ${GIT_SHA1}")
   endif()
 else()
   set(GIT_SHA1 "")
-  if(EXISTS "${LEAN_SOURCE_DIR}/bin/package_version")
-    file(STRINGS "${LEAN_SOURCE_DIR}/bin/package_version" LEAN_PACKAGE_VERSION)
-    message(STATUS "Package version detected: ${LEAN_PACKAGE_VERSION}")
-  endif()
 endif()
 configure_file("${LEAN_SOURCE_DIR}/githash.h.in" "${LEAN_BINARY_DIR}/githash.h")
 
@@ -447,12 +443,13 @@ include_directories(${LEAN_SOURCE_DIR})
 include_directories(${CMAKE_BINARY_DIR})  # version.h etc., "private" headers
 include_directories(${CMAKE_BINARY_DIR}/include)  # config.h etc., "public" headers
 
+# Use CMake profile C++ flags for building Lean libraries, but do not embed in `leanc`
 string(TOUPPER "${CMAKE_BUILD_TYPE}" uppercase_CMAKE_BUILD_TYPE)
-# These are used in lean.mk (and libleanrt) and passed through by stdlib.make
-# They are not embedded into `leanc` since they are build profile/machine specific
 string(APPEND LEANC_OPTS " ${CMAKE_CXX_FLAGS_${uppercase_CMAKE_BUILD_TYPE}}")
+
+# Do embed flag for finding system libraries in dev builds
 if(CMAKE_OSX_SYSROOT AND NOT LEAN_STANDALONE)
-  string(APPEND LEANC_OPTS " ${CMAKE_CXX_SYSROOT_FLAG}${CMAKE_OSX_SYSROOT}")
+  string(APPEND LEANC_EXTRA_FLAGS " ${CMAKE_CXX_SYSROOT_FLAG}${CMAKE_OSX_SYSROOT}")
 endif()
 
 if(${STAGE} GREATER 1)
@@ -504,13 +501,25 @@ string(REGEX REPLACE "^([a-zA-Z]):" "/\\1" LEAN_BIN "${CMAKE_BINARY_DIR}/bin")
 # (also looks nicer in the build log)
 file(RELATIVE_PATH LIB ${LEAN_SOURCE_DIR} ${CMAKE_BINARY_DIR}/lib)
 
+# set up libInit_shared only on Windows; see also stdlib.make.in
+if(${CMAKE_SYSTEM_NAME} MATCHES "Windows")
+  set(INIT_SHARED_LINKER_FLAGS "-Wl,--whole-archive ${CMAKE_BINARY_DIR}/lib/temp/libInit.a.export ${CMAKE_BINARY_DIR}/runtime/libleanrt_initial-exec.a -Wl,--no-whole-archive -Wl,--out-implib,${CMAKE_BINARY_DIR}/lib/lean/libInit_shared.dll.a")
+endif()
+
 if(${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
   set(LEANSHARED_LINKER_FLAGS "-Wl,-force_load,${CMAKE_BINARY_DIR}/lib/lean/libInit.a -Wl,-force_load,${CMAKE_BINARY_DIR}/lib/lean/libLean.a -Wl,-force_load,${CMAKE_BINARY_DIR}/lib/lean/libleancpp.a ${CMAKE_BINARY_DIR}/runtime/libleanrt_initial-exec.a ${LEANSHARED_LINKER_FLAGS}")
+elseif(${CMAKE_SYSTEM_NAME} MATCHES "Windows")
+  set(LEANSHARED_LINKER_FLAGS "-Wl,--whole-archive ${CMAKE_BINARY_DIR}/lib/temp/libLean.a.export -lleancpp -Wl,--no-whole-archive -lInit_shared -Wl,--out-implib,${CMAKE_BINARY_DIR}/lib/lean/libleanshared.dll.a")
 else()
   set(LEANSHARED_LINKER_FLAGS "-Wl,--whole-archive -lInit -lLean -lleancpp -Wl,--no-whole-archive ${CMAKE_BINARY_DIR}/runtime/libleanrt_initial-exec.a ${LEANSHARED_LINKER_FLAGS}")
-  if(${CMAKE_SYSTEM_NAME} MATCHES "Windows")
-    string(APPEND LEANSHARED_LINKER_FLAGS " -Wl,--out-implib,${CMAKE_BINARY_DIR}/lib/lean/libleanshared.dll.a")
-  endif()
+endif()
+
+if (${CMAKE_SYSTEM_NAME} MATCHES "Emscripten")
+  # We do not use dynamic linking via leanshared for Emscripten to keep things
+  # simple. (And we are not interested in `Lake` anyway.) To use dynamic
+  # linking, we would probably have to set MAIN_MODULE=2 on `leanshared`,
+  # SIDE_MODULE=2 on `lean`, and set CMAKE_SHARED_LIBRARY_SUFFIX to ".js".
+  string(APPEND LEAN_EXE_LINKER_FLAGS " ${TOOLCHAIN_STATIC_LINKER_FLAGS} ${EMSCRIPTEN_SETTINGS} -lnodefs.js -s EXIT_RUNTIME=1 -s MAIN_MODULE=1 -s LINKABLE=1 -s EXPORT_ALL=1")
 endif()
 
 # Build the compiler using the bootstrapped C sources for stage0, and use
@@ -519,10 +528,6 @@ if (LLVM AND ${STAGE} GREATER 0)
   set(EXTRA_LEANMAKE_OPTS "LLVM=1")
 endif()
 
-# Escape for `make`. Yes, twice.
-string(REPLACE "$" "$$" CMAKE_EXE_LINKER_FLAGS_MAKE "${CMAKE_EXE_LINKER_FLAGS}")
-string(REPLACE "$" "$$" CMAKE_EXE_LINKER_FLAGS_MAKE_MAKE "${CMAKE_EXE_LINKER_FLAGS_MAKE}")
-configure_file(${LEAN_SOURCE_DIR}/stdlib.make.in ${CMAKE_BINARY_DIR}/stdlib.make)
 add_custom_target(make_stdlib ALL
   WORKING_DIRECTORY ${LEAN_SOURCE_DIR}
   # The actual rule is in a separate makefile because we want to prefix it with '+' to use the Make job server
@@ -540,13 +545,33 @@ endif()
 # We declare these as separate custom targets so they use separate `make` invocations, which makes `make` recompute which dependencies
 # (e.g. `libLean.a`) are now newer than the target file
 
-add_custom_target(leanshared ALL
-  WORKING_DIRECTORY ${LEAN_SOURCE_DIR}
-  DEPENDS make_stdlib leancpp leanrt_initial-exec
-  COMMAND $(MAKE) -f ${CMAKE_BINARY_DIR}/stdlib.make leanshared
-  VERBATIM)
+if(${CMAKE_SYSTEM_NAME} MATCHES "Emscripten")
+  # dummy targets, see `MAIN_MODULE` discussion above
+  add_custom_target(Init_shared ALL
+    DEPENDS make_stdlib leanrt_initial-exec
+    COMMAND touch ${CMAKE_LIBRARY_OUTPUT_DIRECTORY}/libInit_shared${CMAKE_SHARED_LIBRARY_SUFFIX}
+  )
+  add_custom_target(leanshared ALL
+    DEPENDS Init_shared leancpp
+    COMMAND touch ${CMAKE_LIBRARY_OUTPUT_DIRECTORY}/libleanshared${CMAKE_SHARED_LIBRARY_SUFFIX}
+  )
+else()
+  add_custom_target(Init_shared ALL
+    WORKING_DIRECTORY ${LEAN_SOURCE_DIR}
+    DEPENDS make_stdlib leanrt_initial-exec
+    COMMAND $(MAKE) -f ${CMAKE_BINARY_DIR}/stdlib.make Init_shared
+    VERBATIM)
 
-if(${STAGE} GREATER 0)
+  add_custom_target(leanshared ALL
+    WORKING_DIRECTORY ${LEAN_SOURCE_DIR}
+    DEPENDS Init_shared leancpp
+    COMMAND $(MAKE) -f ${CMAKE_BINARY_DIR}/stdlib.make leanshared
+    VERBATIM)
+
+  string(APPEND CMAKE_EXE_LINKER_FLAGS " -lInit_shared -lleanshared")
+endif()
+
+if(${STAGE} GREATER 0 AND NOT ${CMAKE_SYSTEM_NAME} MATCHES "Emscripten")
   if(NOT EXISTS ${LEAN_SOURCE_DIR}/lake/Lake.lean)
     message(FATAL_ERROR "src/lake does not exist. Please check out the Lake submodule using `git submodule update --init src/lake`.")
   endif()
@@ -567,7 +592,7 @@ endif()
 
 # use Bash version for building, use Lean version in bin/ for tests & distribution
 configure_file("${LEAN_SOURCE_DIR}/bin/leanc.in" "${CMAKE_BINARY_DIR}/leanc.sh" @ONLY)
-if(${STAGE} GREATER 0 AND EXISTS ${LEAN_SOURCE_DIR}/Leanc.lean)
+if(${STAGE} GREATER 0 AND EXISTS ${LEAN_SOURCE_DIR}/Leanc.lean AND NOT ${CMAKE_SYSTEM_NAME} MATCHES "Emscripten")
   configure_file("${LEAN_SOURCE_DIR}/Leanc.lean" "${CMAKE_BINARY_DIR}/leanc/Leanc.lean" @ONLY)
   add_custom_target(leanc ALL
     WORKING_DIRECTORY ${CMAKE_BINARY_DIR}/leanc
@@ -618,3 +643,8 @@ if(LEAN_INSTALL_PREFIX)
   set(LEAN_INSTALL_SUFFIX "-${LOWER_SYSTEM_NAME}" CACHE STRING "If LEAN_INSTALL_PREFIX is set, append this value to CMAKE_INSTALL_PREFIX")
   set(CMAKE_INSTALL_PREFIX "${LEAN_INSTALL_PREFIX}/lean-${LEAN_VERSION_STRING}${LEAN_INSTALL_SUFFIX}")
 endif()
+
+# Escape for `make`. Yes, twice.
+string(REPLACE "$" "$$" CMAKE_EXE_LINKER_FLAGS_MAKE "${CMAKE_EXE_LINKER_FLAGS}")
+string(REPLACE "$" "$$" CMAKE_EXE_LINKER_FLAGS_MAKE_MAKE "${CMAKE_EXE_LINKER_FLAGS_MAKE}")
+configure_file(${LEAN_SOURCE_DIR}/stdlib.make.in ${CMAKE_BINARY_DIR}/stdlib.make)

src/Init.lean

@@ -7,6 +7,9 @@ prelude
 import Init.Prelude
 import Init.Notation
 import Init.Tactics
+import Init.TacticsExtra
+import Init.ByCases
+import Init.RCases
 import Init.Core
 import Init.Control
 import Init.Data.Basic
@@ -17,9 +20,16 @@ import Init.System
 import Init.Util
 import Init.Dynamic
 import Init.ShareCommon
+import Init.MetaTypes
 import Init.Meta
 import Init.NotationExtra
 import Init.SimpLemmas
+import Init.PropLemmas
 import Init.Hints
 import Init.Conv
+import Init.Guard
+import Init.Simproc
 import Init.SizeOfLemmas
+import Init.BinderPredicates
+import Init.Ext
+import Init.Omega

src/Init/BinderPredicates.lean

@@ -0,0 +1,82 @@
+/-
+Copyright (c) 2021 Microsoft Corporation. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Gabriel Ebner
+-/
+prelude
+import Init.NotationExtra
+
+namespace Lean
+
+/--
+The syntax category of binder predicates contains predicates like `> 0`, `∈ s`, etc.
+(`: t` should not be a binder predicate because it would clash with the built-in syntax for ∀/∃.)
+-/
+declare_syntax_cat binderPred
+
+/--
+`satisfies_binder_pred% t pred` expands to a proposition expressing that `t` satisfies `pred`.
+-/
+syntax "satisfies_binder_pred% " term:max binderPred : term
+
+-- Extend ∀ and ∃ to binder predicates.
+
+/--
+The notation `∃ x < 2, p x` is shorthand for `∃ x, x < 2 ∧ p x`,
+and similarly for other binary operators.
+-/
+syntax "∃ " binderIdent binderPred ", " term : term
+/--
+The notation `∀ x < 2, p x` is shorthand for `∀ x, x < 2 → p x`,
+and similarly for other binary operators.
+-/
+syntax "∀ " binderIdent binderPred ", " term : term
+
+macro_rules
+  | `(∃ $x:ident $pred:binderPred, $p) =>
+    `(∃ $x:ident, satisfies_binder_pred% $x $pred ∧ $p)
+  | `(∃ _ $pred:binderPred, $p) =>
+    `(∃ x, satisfies_binder_pred% x $pred ∧ $p)
+
+macro_rules
+  | `(∀ $x:ident $pred:binderPred, $p) =>
+    `(∀ $x:ident, satisfies_binder_pred% $x $pred → $p)
+  | `(∀ _ $pred:binderPred, $p) =>
+    `(∀ x, satisfies_binder_pred% x $pred → $p)
+
+/-- Declare `∃ x > y, ...` as syntax for `∃ x, x > y ∧ ...` -/
+binder_predicate x " > " y:term => `($x > $y)
+/-- Declare `∃ x ≥ y, ...` as syntax for `∃ x, x ≥ y ∧ ...` -/
+binder_predicate x " ≥ " y:term => `($x ≥ $y)
+/-- Declare `∃ x < y, ...` as syntax for `∃ x, x < y ∧ ...` -/
+binder_predicate x " < " y:term => `($x < $y)
+/-- Declare `∃ x ≤ y, ...` as syntax for `∃ x, x ≤ y ∧ ...` -/
+binder_predicate x " ≤ " y:term => `($x ≤ $y)
+/-- Declare `∃ x ≠ y, ...` as syntax for `∃ x, x ≠ y ∧ ...` -/
+binder_predicate x " ≠ " y:term => `($x ≠ $y)
+
+/-- Declare `∀ x ∈ y, ...` as syntax for `∀ x, x ∈ y → ...` and `∃ x ∈ y, ...` as syntax for
+`∃ x, x ∈ y ∧ ...` -/
+binder_predicate x " ∈ " y:term => `($x ∈ $y)
+
+/-- Declare `∀ x ∉ y, ...` as syntax for `∀ x, x ∉ y → ...` and `∃ x ∉ y, ...` as syntax for
+`∃ x, x ∉ y ∧ ...` -/
+binder_predicate x " ∉ " y:term => `($x ∉ $y)
+
+/-- Declare `∀ x ⊆ y, ...` as syntax for `∀ x, x ⊆ y → ...` and `∃ x ⊆ y, ...` as syntax for
+`∃ x, x ⊆ y ∧ ...` -/
+binder_predicate x " ⊆ " y:term => `($x ⊆ $y)
+
+/-- Declare `∀ x ⊂ y, ...` as syntax for `∀ x, x ⊂ y → ...` and `∃ x ⊂ y, ...` as syntax for
+`∃ x, x ⊂ y ∧ ...` -/
+binder_predicate x " ⊂ " y:term => `($x ⊂ $y)
+
+/-- Declare `∀ x ⊇ y, ...` as syntax for `∀ x, x ⊇ y → ...` and `∃ x ⊇ y, ...` as syntax for
+`∃ x, x ⊇ y ∧ ...` -/
+binder_predicate x " ⊇ " y:term => `($x ⊇ $y)
+
+/-- Declare `∀ x ⊃ y, ...` as syntax for `∀ x, x ⊃ y → ...` and `∃ x ⊃ y, ...` as syntax for
+`∃ x, x ⊃ y ∧ ...` -/
+binder_predicate x " ⊃ " y:term => `($x ⊃ $y)
+
+end Lean

src/Init/ByCases.lean

@@ -0,0 +1,65 @@
+/-
+Copyright (c) 2024 Lean FRO, LLC. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Leonardo de Moura, Mario Carneiro
+-/
+prelude
+import Init.Classical
+
+/-! # by_cases tactic and if-then-else support -/
+
+/--
+`by_cases (h :)? p` splits the main goal into two cases, assuming `h : p` in the first branch, and `h : ¬ p` in the second branch.
+-/
+syntax "by_cases " (atomic(ident " : "))? term : tactic
+
+macro_rules
+  | `(tactic| by_cases $e) => `(tactic| by_cases h : $e)
+macro_rules
+  | `(tactic| by_cases $h : $e) =>
+    `(tactic| open Classical in refine if $h:ident : $e then ?pos else ?neg)
+
+/-! ## if-then-else -/
+
+@[simp] theorem if_true {_ : Decidable True} (t e : α) : ite True t e = t := if_pos trivial
+
+@[simp] theorem if_false {_ : Decidable False} (t e : α) : ite False t e = e := if_neg id
+
+theorem ite_id [Decidable c] {α} (t : α) : (if c then t else t) = t := by split <;> rfl
+
+/-- A function applied to a `dite` is a `dite` of that function applied to each of the branches. -/
+theorem apply_dite (f : α → β) (P : Prop) [Decidable P] (x : P → α) (y : ¬P → α) :
+    f (dite P x y) = dite P (fun h => f (x h)) (fun h => f (y h)) := by
+  by_cases h : P <;> simp [h]
+
+/-- A function applied to a `ite` is a `ite` of that function applied to each of the branches. -/
+theorem apply_ite (f : α → β) (P : Prop) [Decidable P] (x y : α) :
+    f (ite P x y) = ite P (f x) (f y) :=
+  apply_dite f P (fun _ => x) (fun _ => y)
+
+@[simp] theorem dite_eq_left_iff {P : Prop} [Decidable P] {B : ¬ P → α} :
+    dite P (fun _ => a) B = a ↔ ∀ h, B h = a := by
+  by_cases P <;> simp [*, forall_prop_of_true, forall_prop_of_false]
+
+@[simp] theorem dite_eq_right_iff {P : Prop} [Decidable P] {A : P → α} :
+    (dite P A fun _ => b) = b ↔ ∀ h, A h = b := by
+  by_cases P <;> simp [*, forall_prop_of_true, forall_prop_of_false]
+
+@[simp] theorem ite_eq_left_iff {P : Prop} [Decidable P] : ite P a b = a ↔ ¬P → b = a :=
+  dite_eq_left_iff
+
+@[simp] theorem ite_eq_right_iff {P : Prop} [Decidable P] : ite P a b = b ↔ P → a = b :=
+  dite_eq_right_iff
+
+/-- A `dite` whose results do not actually depend on the condition may be reduced to an `ite`. -/
+@[simp] theorem dite_eq_ite [Decidable P] : (dite P (fun _ => a) fun _ => b) = ite P a b := rfl
+
+-- We don't mark this as `simp` as it is already handled by `ite_eq_right_iff`.
+theorem ite_some_none_eq_none [Decidable P] :
+    (if P then some x else none) = none ↔ ¬ P := by
+  simp only [ite_eq_right_iff]
+  rfl
+
+@[simp] theorem ite_some_none_eq_some [Decidable P] :
+    (if P then some x else none) = some y ↔ P ∧ x = y := by
+  split <;> simp_all

src/Init/Classical.lean

@@ -1,11 +1,10 @@
 /-
 Copyright (c) 2020 Microsoft Corporation. All rights reserved.
 Released under Apache 2.0 license as described in the file LICENSE.
-Authors: Leonardo de Moura
+Authors: Leonardo de Moura, Mario Carneiro
 -/
 prelude
-import Init.Core
-import Init.NotationExtra
+import Init.PropLemmas
 
 universe u v
 
@@ -22,7 +21,7 @@ noncomputable def choose {α : Sort u} {p : α → Prop} (h : ∃ x, p x) : α :
 theorem choose_spec {α : Sort u} {p : α → Prop} (h : ∃ x, p x) : p (choose h) :=
   (indefiniteDescription p h).property
 
-/-- Diaconescu's theorem: excluded middle from choice, Function extensionality and propositional extensionality. -/
+/-- **Diaconescu's theorem**: excluded middle from choice, Function extensionality and propositional extensionality. -/
 theorem em (p : Prop) : p ∨ ¬p :=
   let U (x : Prop) : Prop := x = True ∨ p
   let V (x : Prop) : Prop := x = False ∨ p
@@ -112,8 +111,8 @@ theorem skolem {α : Sort u} {b : α → Sort v} {p : ∀ x, b x → Prop} : (
 
 theorem propComplete (a : Prop) : a = True ∨ a = False :=
   match em a with
-  | Or.inl ha => Or.inl (propext (Iff.intro (fun _ => ⟨⟩) (fun _ => ha)))
-  | Or.inr hn => Or.inr (propext (Iff.intro (fun h => hn h) (fun h => False.elim h)))
+  | Or.inl ha => Or.inl (eq_true ha)
+  | Or.inr hn => Or.inr (eq_false hn)
 
 -- this supercedes byCases in Decidable
 theorem byCases {p q : Prop} (hpq : p → q) (hnpq : ¬p → q) : q :=
@@ -123,21 +122,49 @@ theorem byCases {p q : Prop} (hpq : p → q) (hnpq : ¬p → q) : q :=
 theorem byContradiction {p : Prop} (h : ¬p → False) : p :=
   Decidable.byContradiction (dec := propDecidable _) h
 
-/--
-`by_cases (h :)? p` splits the main goal into two cases, assuming `h : p` in the first branch, and `h : ¬ p` in the second branch.
--/
-syntax "by_cases " (atomic(ident " : "))? term : tactic
+/-- The Double Negation Theorem: `¬¬P` is equivalent to `P`.
+The left-to-right direction, double negation elimination (DNE),
+is classically true but not constructively. -/
+@[simp] theorem not_not : ¬¬a ↔ a := Decidable.not_not
 
-macro_rules
-  | `(tactic| by_cases $h : $e) =>
-    `(tactic|
-      cases em $e with
-      | inl $h => _
-      | inr $h => _)
-  | `(tactic| by_cases $e) =>
-    `(tactic|
-      cases em $e with
-      | inl h => _
-      | inr h => _)
+@[simp low] theorem not_forall {p : α → Prop} : (¬∀ x, p x) ↔ ∃ x, ¬p x := Decidable.not_forall
+
+theorem not_forall_not {p : α → Prop} : (¬∀ x, ¬p x) ↔ ∃ x, p x := Decidable.not_forall_not
+theorem not_exists_not {p : α → Prop} : (¬∃ x, ¬p x) ↔ ∀ x, p x := Decidable.not_exists_not
+
+theorem forall_or_exists_not (P : α → Prop) : (∀ a, P a) ∨ ∃ a, ¬ P a := by
+  rw [← not_forall]; exact em _
+theorem exists_or_forall_not (P : α → Prop) : (∃ a, P a) ∨ ∀ a, ¬ P a := by
+  rw [← not_exists]; exact em _
+
+theorem or_iff_not_imp_left  : a ∨ b ↔ (¬a → b) := Decidable.or_iff_not_imp_left
+theorem or_iff_not_imp_right : a ∨ b ↔ (¬b → a) := Decidable.or_iff_not_imp_right
+
+theorem not_imp_iff_and_not : ¬(a → b) ↔ a ∧ ¬b := Decidable.not_imp_iff_and_not
+
+theorem not_and_iff_or_not_not : ¬(a ∧ b) ↔ ¬a ∨ ¬b := Decidable.not_and_iff_or_not_not
+
+theorem not_iff : ¬(a ↔ b) ↔ (¬a ↔ b) := Decidable.not_iff
+
+@[simp] theorem imp_iff_left_iff  : (b ↔ a → b) ↔ a ∨ b := Decidable.imp_iff_left_iff
+@[simp] theorem imp_iff_right_iff : (a → b ↔ b) ↔ a ∨ b := Decidable.imp_iff_right_iff
+
+@[simp] theorem and_or_imp : a ∧ b ∨ (a → c) ↔ a → b ∨ c := Decidable.and_or_imp
+
+@[simp] theorem not_imp : ¬(a → b) ↔ a ∧ ¬b := Decidable.not_imp_iff_and_not
+
+@[simp] theorem imp_and_neg_imp_iff (p q : Prop) : (p → q) ∧ (¬p → q) ↔ q :=
+  Iff.intro (fun (a : _ ∧ _) => (Classical.em p).rec a.left a.right)
+            (fun a => And.intro (fun _ => a) (fun _ => a))
 
 end Classical
+
+/- Export for Mathlib compat. -/
+export Classical (imp_iff_right_iff imp_and_neg_imp_iff and_or_imp not_imp)
+
+/-- Extract an element from a existential statement, using `Classical.choose`. -/
+-- This enables projection notation.
+@[reducible] noncomputable def Exists.choose {p : α → Prop} (P : ∃ a, p a) : α := Classical.choose P
+
+/-- Show that an element extracted from `P : ∃ a, p a` using `P.choose` satisfies `p`. -/
+theorem Exists.choose_spec {p : α → Prop} (P : ∃ a, p a) : p P.choose := Classical.choose_spec P

src/Init/Coe.lean

@@ -290,6 +290,12 @@ between e.g. `↑x + ↑y` and `↑(x + y)`.
 -/
 syntax:1024 (name := coeNotation) "↑" term:1024 : term
 
+/-- `⇑ t` coerces `t` to a function. -/
+syntax:1024 (name := coeFunNotation) "⇑" term:1024 : term
+
+/-- `↥ t` coerces `t` to a type. -/
+syntax:1024 (name := coeSortNotation) "↥" term:1024 : term
+
 /-! # Basic instances -/
 
 instance boolToProp : Coe Bool Prop where
@@ -315,7 +321,7 @@ Helper definition used by the elaborator. It is not meant to be used directly by
 This is used for coercions between monads, in the case where we want to apply
 a monad lift and a coercion on the result type at the same time.
 -/
-@[inline, coe_decl] def Lean.Internal.liftCoeM {m : Type u → Type v} {n : Type u → Type w} {α β : Type u}
+@[coe_decl] abbrev Lean.Internal.liftCoeM {m : Type u → Type v} {n : Type u → Type w} {α β : Type u}
     [MonadLiftT m n] [∀ a, CoeT α a β] [Monad n] (x : m α) : n β := do
   let a ← liftM x
   pure (CoeT.coe a)
@@ -325,7 +331,7 @@ Helper definition used by the elaborator. It is not meant to be used directly by
 
 This is used for coercing the result type under a monad.
 -/
-@[inline, coe_decl] def Lean.Internal.coeM {m : Type u → Type v} {α β : Type u}
+@[coe_decl] abbrev Lean.Internal.coeM {m : Type u → Type v} {α β : Type u}
     [∀ a, CoeT α a β] [Monad m] (x : m α) : m β := do
   let a ← x
   pure (CoeT.coe a)

src/Init/Control/ExceptCps.lean

@@ -4,7 +4,7 @@ Released under Apache 2.0 license as described in the file LICENSE.
 Authors: Leonardo de Moura
 -/
 prelude
-import Init.Control.Lawful
+import Init.Control.Lawful.Basic
 
 /-!
 The Exception monad transformer using CPS style.
@@ -18,6 +18,7 @@ namespace ExceptCpsT
 def run {ε α : Type u} [Monad m] (x : ExceptCpsT ε m α) : m (Except ε α) :=
   x _ (fun a => pure (Except.ok a)) (fun e => pure (Except.error e))
 
+set_option linter.unusedVariables false in  -- `s` unused
 @[always_inline, inline]
 def runK {ε α : Type u} (x : ExceptCpsT ε m α) (s : ε) (ok : α → m β) (error : ε → m β) : m β :=
   x _ ok error

src/Init/Control/Lawful.lean

@@ -1,309 +1,8 @@
 /-
 Copyright (c) 2021 Microsoft Corporation. All rights reserved.
 Released under Apache 2.0 license as described in the file LICENSE.
-Authors: Sebastian Ullrich, Leonardo de Moura
+Authors: Sebastian Ullrich, Leonardo de Moura, Mario Carneiro
 -/
 prelude
-import Init.SimpLemmas
-import Init.Control.Except
-import Init.Control.StateRef
-
-open Function
-
-@[simp] theorem monadLift_self [Monad m] (x : m α) : monadLift x = x :=
-  rfl
-
-class LawfulFunctor (f : Type u → Type v) [Functor f] : Prop where
-  map_const          : (Functor.mapConst : α → f β → f α) = Functor.map ∘ const β
-  id_map   (x : f α) : id <$> x = x
-  comp_map (g : α → β) (h : β → γ) (x : f α) : (h ∘ g) <$> x = h <$> g <$> x
-
-export LawfulFunctor (map_const id_map comp_map)
-
-attribute [simp] id_map
-
-@[simp] theorem id_map' [Functor m] [LawfulFunctor m] (x : m α) : (fun a => a) <$> x = x :=
-  id_map x
-
-class LawfulApplicative (f : Type u → Type v) [Applicative f] extends LawfulFunctor f : Prop where
-  seqLeft_eq  (x : f α) (y : f β)     : x <* y = const β <$> x <*> y
-  seqRight_eq (x : f α) (y : f β)     : x *> y = const α id <$> x <*> y
-  pure_seq    (g : α → β) (x : f α)   : pure g <*> x = g <$> x
-  map_pure    (g : α → β) (x : α)     : g <$> (pure x : f α) = pure (g x)
-  seq_pure    {α β : Type u} (g : f (α → β)) (x : α) : g <*> pure x = (fun h => h x) <$> g
-  seq_assoc   {α β γ : Type u} (x : f α) (g : f (α → β)) (h : f (β → γ)) : h <*> (g <*> x) = ((@comp α β γ) <$> h) <*> g <*> x
-  comp_map g h x := (by
-    repeat rw [← pure_seq]
-    simp [seq_assoc, map_pure, seq_pure])
-
-export LawfulApplicative (seqLeft_eq seqRight_eq pure_seq map_pure seq_pure seq_assoc)
-
-attribute [simp] map_pure seq_pure
-
-@[simp] theorem pure_id_seq [Applicative f] [LawfulApplicative f] (x : f α) : pure id <*> x = x := by
-  simp [pure_seq]
-
-class LawfulMonad (m : Type u → Type v) [Monad m] extends LawfulApplicative m : Prop where
-  bind_pure_comp (f : α → β) (x : m α) : x >>= (fun a => pure (f a)) = f <$> x
-  bind_map       {α β : Type u} (f : m (α → β)) (x : m α) : f >>= (. <$> x) = f <*> x
-  pure_bind      (x : α) (f : α → m β) : pure x >>= f = f x
-  bind_assoc     (x : m α) (f : α → m β) (g : β → m γ) : x >>= f >>= g = x >>= fun x => f x >>= g
-  map_pure g x    := (by rw [← bind_pure_comp, pure_bind])
-  seq_pure g x    := (by rw [← bind_map]; simp [map_pure, bind_pure_comp])
-  seq_assoc x g h := (by simp [← bind_pure_comp, ← bind_map, bind_assoc, pure_bind])
-
-export LawfulMonad (bind_pure_comp bind_map pure_bind bind_assoc)
-attribute [simp] pure_bind bind_assoc
-
-@[simp] theorem bind_pure [Monad m] [LawfulMonad m] (x : m α) : x >>= pure = x := by
-  show x >>= (fun a => pure (id a)) = x
-  rw [bind_pure_comp, id_map]
-
-theorem map_eq_pure_bind [Monad m] [LawfulMonad m] (f : α → β) (x : m α) : f <$> x = x >>= fun a => pure (f a) := by
-  rw [← bind_pure_comp]
-
-theorem seq_eq_bind_map {α β : Type u} [Monad m] [LawfulMonad m] (f : m (α → β)) (x : m α) : f <*> x = f >>= (. <$> x) := by
-  rw [← bind_map]
-
-theorem bind_congr [Bind m] {x : m α} {f g : α → m β} (h : ∀ a, f a = g a) : x >>= f = x >>= g := by
-  simp [funext h]
-
-@[simp] theorem bind_pure_unit [Monad m] [LawfulMonad m] {x : m PUnit} : (x >>= fun _ => pure ⟨⟩) = x := by
-  rw [bind_pure]
-
-theorem map_congr [Functor m] {x : m α} {f g : α → β} (h : ∀ a, f a = g a) : (f <$> x : m β) = g <$> x := by
-  simp [funext h]
-
-theorem seq_eq_bind {α β : Type u} [Monad m] [LawfulMonad m] (mf : m (α → β)) (x : m α) : mf <*> x = mf >>= fun f => f <$> x := by
-  rw [bind_map]
-
-theorem seqRight_eq_bind [Monad m] [LawfulMonad m] (x : m α) (y : m β) : x *> y = x >>= fun _ => y := by
-  rw [seqRight_eq]
-  simp [map_eq_pure_bind, seq_eq_bind_map, const]
-
-theorem seqLeft_eq_bind [Monad m] [LawfulMonad m] (x : m α) (y : m β) : x <* y = x >>= fun a => y >>= fun _ => pure a := by
-  rw [seqLeft_eq]; simp [map_eq_pure_bind, seq_eq_bind_map]
-
-/-! # Id -/
-
-namespace Id
-
-@[simp] theorem map_eq (x : Id α) (f : α → β) : f <$> x = f x := rfl
-@[simp] theorem bind_eq (x : Id α) (f : α → id β) : x >>= f = f x := rfl
-@[simp] theorem pure_eq (a : α) : (pure a : Id α) = a := rfl
-
-instance : LawfulMonad Id := by
-  refine' { .. } <;> intros <;> rfl
-
-end Id
-
-/-! # ExceptT -/
-
-namespace ExceptT
-
-theorem ext [Monad m] {x y : ExceptT ε m α} (h : x.run = y.run) : x = y := by
-  simp [run] at h
-  assumption
-
-@[simp] theorem run_pure [Monad m] (x : α) : run (pure x : ExceptT ε m α) = pure (Except.ok x) := rfl
-
-@[simp] theorem run_lift  [Monad.{u, v} m] (x : m α) : run (ExceptT.lift x : ExceptT ε m α) = (Except.ok <$> x : m (Except ε α)) := rfl
-
-@[simp] theorem run_throw [Monad m] : run (throw e : ExceptT ε m β) = pure (Except.error e) := rfl
-
-@[simp] theorem run_bind_lift [Monad m] [LawfulMonad m] (x : m α) (f : α → ExceptT ε m β) : run (ExceptT.lift x >>= f : ExceptT ε m β) = x >>= fun a => run (f a) := by
-  simp[ExceptT.run, ExceptT.lift, bind, ExceptT.bind, ExceptT.mk, ExceptT.bindCont, map_eq_pure_bind]
-
-@[simp] theorem bind_throw [Monad m] [LawfulMonad m] (f : α → ExceptT ε m β) : (throw e >>= f) = throw e := by
-  simp [throw, throwThe, MonadExceptOf.throw, bind, ExceptT.bind, ExceptT.bindCont, ExceptT.mk]
-
-theorem run_bind [Monad m] (x : ExceptT ε m α)
-        : run (x >>= f : ExceptT ε m β)
-          =
-          run x >>= fun
-                     | Except.ok x => run (f x)
-                     | Except.error e => pure (Except.error e) :=
-  rfl
-
-@[simp] theorem lift_pure [Monad m] [LawfulMonad m] (a : α) : ExceptT.lift (pure a) = (pure a : ExceptT ε m α) := by
-  simp [ExceptT.lift, pure, ExceptT.pure]
-
-@[simp] theorem run_map [Monad m] [LawfulMonad m] (f : α → β) (x : ExceptT ε m α)
-    : (f <$> x).run = Except.map f <$> x.run := by
-  simp [Functor.map, ExceptT.map, map_eq_pure_bind]
-  apply bind_congr
-  intro a; cases a <;> simp [Except.map]
-
-protected theorem seq_eq {α β ε : Type u} [Monad m] (mf : ExceptT ε m (α → β)) (x : ExceptT ε m α) : mf <*> x = mf >>= fun f => f <$> x :=
-  rfl
-
-protected theorem bind_pure_comp [Monad m] [LawfulMonad m] (f : α → β) (x : ExceptT ε m α) : x >>= pure ∘ f = f <$> x := by
-  intros; rfl
-
-protected theorem seqLeft_eq {α β ε : Type u} {m : Type u → Type v} [Monad m] [LawfulMonad m] (x : ExceptT ε m α) (y : ExceptT ε m β) : x <* y = const β <$> x <*> y := by
-  show (x >>= fun a => y >>= fun _ => pure a) = (const (α := α) β <$> x) >>= fun f => f <$> y
-  rw [← ExceptT.bind_pure_comp]
-  apply ext
-  simp [run_bind]
-  apply bind_congr
-  intro
-  | Except.error _ => simp
-  | Except.ok _ =>
-    simp [map_eq_pure_bind]; apply bind_congr; intro b;
-    cases b <;> simp [comp, Except.map, const]
-
-protected theorem seqRight_eq [Monad m] [LawfulMonad m] (x : ExceptT ε m α) (y : ExceptT ε m β) : x *> y = const α id <$> x <*> y := by
-  show (x >>= fun _ => y) = (const α id <$> x) >>= fun f => f <$> y
-  rw [← ExceptT.bind_pure_comp]
-  apply ext
-  simp [run_bind]
-  apply bind_congr
-  intro a; cases a <;> simp
-
-instance [Monad m] [LawfulMonad m] : LawfulMonad (ExceptT ε m) where
-  id_map         := by intros; apply ext; simp
-  map_const      := by intros; rfl
-  seqLeft_eq     := ExceptT.seqLeft_eq
-  seqRight_eq    := ExceptT.seqRight_eq
-  pure_seq       := by intros; apply ext; simp [ExceptT.seq_eq, run_bind]
-  bind_pure_comp := ExceptT.bind_pure_comp
-  bind_map       := by intros; rfl
-  pure_bind      := by intros; apply ext; simp [run_bind]
-  bind_assoc     := by intros; apply ext; simp [run_bind]; apply bind_congr; intro a; cases a <;> simp
-
-end ExceptT
-
-/-! # ReaderT -/
-
-namespace ReaderT
-
-theorem ext {x y : ReaderT ρ m α} (h : ∀ ctx, x.run ctx = y.run ctx) : x = y := by
-  simp [run] at h
-  exact funext h
-
-@[simp] theorem run_pure [Monad m] (a : α) (ctx : ρ) : (pure a : ReaderT ρ m α).run ctx = pure a := rfl
-
-@[simp] theorem run_bind [Monad m] (x : ReaderT ρ m α) (f : α → ReaderT ρ m β) (ctx : ρ)
-    : (x >>= f).run ctx = x.run ctx >>= λ a => (f a).run ctx := rfl
-
-@[simp] theorem run_mapConst [Monad m] (a : α) (x : ReaderT ρ m β) (ctx : ρ)
-    : (Functor.mapConst a x).run ctx = Functor.mapConst a (x.run ctx) := rfl
-
-@[simp] theorem run_map [Monad m] (f : α → β) (x : ReaderT ρ m α) (ctx : ρ)
-    : (f <$> x).run ctx = f <$> x.run ctx := rfl
-
-@[simp] theorem run_monadLift [MonadLiftT n m] (x : n α) (ctx : ρ)
-    : (monadLift x : ReaderT ρ m α).run ctx = (monadLift x : m α) := rfl
-
-@[simp] theorem run_monadMap [MonadFunctor n m] (f : {β : Type u} → n β → n β) (x : ReaderT ρ m α) (ctx : ρ)
-    : (monadMap @f x : ReaderT ρ m α).run ctx = monadMap @f (x.run ctx) := rfl
-
-@[simp] theorem run_read [Monad m] (ctx : ρ) : (ReaderT.read : ReaderT ρ m ρ).run ctx = pure ctx := rfl
-
-@[simp] theorem run_seq {α β : Type u} [Monad m] (f : ReaderT ρ m (α → β)) (x : ReaderT ρ m α) (ctx : ρ)
-    : (f <*> x).run ctx = (f.run ctx <*> x.run ctx) := rfl
-
-@[simp] theorem run_seqRight [Monad m] (x : ReaderT ρ m α) (y : ReaderT ρ m β) (ctx : ρ)
-    : (x *> y).run ctx = (x.run ctx *> y.run ctx) := rfl
-
-@[simp] theorem run_seqLeft [Monad m] (x : ReaderT ρ m α) (y : ReaderT ρ m β) (ctx : ρ)
-    : (x <* y).run ctx = (x.run ctx <* y.run ctx) := rfl
-
-instance [Monad m] [LawfulFunctor m] : LawfulFunctor (ReaderT ρ m) where
-  id_map    := by intros; apply ext; simp
-  map_const := by intros; funext a b; apply ext; intros; simp [map_const]
-  comp_map  := by intros; apply ext; intros; simp [comp_map]
-
-instance [Monad m] [LawfulApplicative m] : LawfulApplicative (ReaderT ρ m) where
-  seqLeft_eq  := by intros; apply ext; intros; simp [seqLeft_eq]
-  seqRight_eq := by intros; apply ext; intros; simp [seqRight_eq]
-  pure_seq    := by intros; apply ext; intros; simp [pure_seq]
-  map_pure    := by intros; apply ext; intros; simp [map_pure]
-  seq_pure    := by intros; apply ext; intros; simp [seq_pure]
-  seq_assoc   := by intros; apply ext; intros; simp [seq_assoc]
-
-instance [Monad m] [LawfulMonad m] : LawfulMonad (ReaderT ρ m) where
-  bind_pure_comp := by intros; apply ext; intros; simp [LawfulMonad.bind_pure_comp]
-  bind_map       := by intros; apply ext; intros; simp [bind_map]
-  pure_bind      := by intros; apply ext; intros; simp
-  bind_assoc     := by intros; apply ext; intros; simp
-
-end ReaderT
-
-/-! # StateRefT -/
-
-instance [Monad m] [LawfulMonad m] : LawfulMonad (StateRefT' ω σ m) :=
-  inferInstanceAs (LawfulMonad (ReaderT (ST.Ref ω σ) m))
-
-/-! # StateT -/
-
-namespace StateT
-
-theorem ext {x y : StateT σ m α} (h : ∀ s, x.run s = y.run s) : x = y :=
-  funext h
-
-@[simp] theorem run'_eq [Monad m] (x : StateT σ m α) (s : σ) : run' x s = (·.1) <$> run x s :=
-  rfl
-
-@[simp] theorem run_pure [Monad m] (a : α) (s : σ) : (pure a : StateT σ m α).run s = pure (a, s) := rfl
-
-@[simp] theorem run_bind [Monad m] (x : StateT σ m α) (f : α → StateT σ m β) (s : σ)
-    : (x >>= f).run s = x.run s >>= λ p => (f p.1).run p.2 := by
-  simp [bind, StateT.bind, run]
-
-@[simp] theorem run_map {α β σ : Type u} [Monad m] [LawfulMonad m] (f : α → β) (x : StateT σ m α) (s : σ) : (f <$> x).run s = (fun (p : α × σ) => (f p.1, p.2)) <$> x.run s := by
-  simp [Functor.map, StateT.map, run, map_eq_pure_bind]
-
-@[simp] theorem run_get [Monad m] (s : σ)    : (get : StateT σ m σ).run s = pure (s, s) := rfl
-
-@[simp] theorem run_set [Monad m] (s s' : σ) : (set s' : StateT σ m PUnit).run s = pure (⟨⟩, s') := rfl
-
-@[simp] theorem run_modify [Monad m] (f : σ → σ) (s : σ) : (modify f : StateT σ m PUnit).run s = pure (⟨⟩, f s) := rfl
-
-@[simp] theorem run_modifyGet [Monad m] (f : σ → α × σ) (s : σ) : (modifyGet f : StateT σ m α).run s = pure ((f s).1, (f s).2) := by
-  simp [modifyGet, MonadStateOf.modifyGet, StateT.modifyGet, run]
-
-@[simp] theorem run_lift {α σ : Type u} [Monad m] (x : m α) (s : σ) : (StateT.lift x : StateT σ m α).run s = x >>= fun a => pure (a, s) := rfl
-
-@[simp] theorem run_bind_lift {α σ : Type u} [Monad m] [LawfulMonad m] (x : m α) (f : α → StateT σ m β) (s : σ) : (StateT.lift x >>= f).run s = x >>= fun a => (f a).run s := by
-  simp [StateT.lift, StateT.run, bind, StateT.bind]
-
-@[simp] theorem run_monadLift {α σ : Type u} [Monad m] [MonadLiftT n m] (x : n α) (s : σ) : (monadLift x : StateT σ m α).run s = (monadLift x : m α) >>= fun a => pure (a, s) := rfl
-
-@[simp] theorem run_monadMap [Monad m] [MonadFunctor n m] (f : {β : Type u} → n β → n β) (x : StateT σ m α) (s : σ)
-    : (monadMap @f x : StateT σ m α).run s = monadMap @f (x.run s) := rfl
-
-@[simp] theorem run_seq {α β σ : Type u} [Monad m] [LawfulMonad m] (f : StateT σ m (α → β)) (x : StateT σ m α) (s : σ) : (f <*> x).run s = (f.run s >>= fun fs => (fun (p : α × σ) => (fs.1 p.1, p.2)) <$> x.run fs.2) := by
-  show (f >>= fun g => g <$> x).run s = _
-  simp
-
-@[simp] theorem run_seqRight [Monad m] [LawfulMonad m] (x : StateT σ m α) (y : StateT σ m β) (s : σ) : (x *> y).run s = (x.run s >>= fun p => y.run p.2) := by
-  show (x >>= fun _ => y).run s = _
-  simp
-
-@[simp] theorem run_seqLeft {α β σ : Type u} [Monad m] [LawfulMonad m] (x : StateT σ m α) (y : StateT σ m β) (s : σ) : (x <* y).run s = (x.run s >>= fun p => y.run p.2 >>= fun p' => pure (p.1, p'.2)) := by
-  show (x >>= fun a => y >>= fun _ => pure a).run s = _
-  simp
-
-theorem seqRight_eq [Monad m] [LawfulMonad m] (x : StateT σ m α) (y : StateT σ m β) : x *> y = const α id <$> x <*> y := by
-  apply ext; intro s
-  simp [map_eq_pure_bind, const]
-  apply bind_congr; intro p; cases p
-  simp [Prod.eta]
-
-theorem seqLeft_eq [Monad m] [LawfulMonad m] (x : StateT σ m α) (y : StateT σ m β) : x <* y = const β <$> x <*> y := by
-  apply ext; intro s
-  simp [map_eq_pure_bind]
-
-instance [Monad m] [LawfulMonad m] : LawfulMonad (StateT σ m) where
-  id_map         := by intros; apply ext; intros; simp[Prod.eta]
-  map_const      := by intros; rfl
-  seqLeft_eq     := seqLeft_eq
-  seqRight_eq    := seqRight_eq
-  pure_seq       := by intros; apply ext; intros; simp
-  bind_pure_comp := by intros; apply ext; intros; simp; apply LawfulMonad.bind_pure_comp
-  bind_map       := by intros; rfl
-  pure_bind      := by intros; apply ext; intros; simp
-  bind_assoc     := by intros; apply ext; intros; simp
-
-end StateT
+import Init.Control.Lawful.Basic
+import Init.Control.Lawful.Instances

src/Init/Control/Lawful/Basic.lean

@@ -0,0 +1,138 @@
+/-
+Copyright (c) 2021 Microsoft Corporation. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Sebastian Ullrich, Leonardo de Moura, Mario Carneiro
+-/
+prelude
+import Init.SimpLemmas
+import Init.Meta
+
+open Function
+
+@[simp] theorem monadLift_self [Monad m] (x : m α) : monadLift x = x :=
+  rfl
+
+class LawfulFunctor (f : Type u → Type v) [Functor f] : Prop where
+  map_const          : (Functor.mapConst : α → f β → f α) = Functor.map ∘ const β
+  id_map   (x : f α) : id <$> x = x
+  comp_map (g : α → β) (h : β → γ) (x : f α) : (h ∘ g) <$> x = h <$> g <$> x
+
+export LawfulFunctor (map_const id_map comp_map)
+
+attribute [simp] id_map
+
+@[simp] theorem id_map' [Functor m] [LawfulFunctor m] (x : m α) : (fun a => a) <$> x = x :=
+  id_map x
+
+class LawfulApplicative (f : Type u → Type v) [Applicative f] extends LawfulFunctor f : Prop where
+  seqLeft_eq  (x : f α) (y : f β)     : x <* y = const β <$> x <*> y
+  seqRight_eq (x : f α) (y : f β)     : x *> y = const α id <$> x <*> y
+  pure_seq    (g : α → β) (x : f α)   : pure g <*> x = g <$> x
+  map_pure    (g : α → β) (x : α)     : g <$> (pure x : f α) = pure (g x)
+  seq_pure    {α β : Type u} (g : f (α → β)) (x : α) : g <*> pure x = (fun h => h x) <$> g
+  seq_assoc   {α β γ : Type u} (x : f α) (g : f (α → β)) (h : f (β → γ)) : h <*> (g <*> x) = ((@comp α β γ) <$> h) <*> g <*> x
+  comp_map g h x := (by
+    repeat rw [← pure_seq]
+    simp [seq_assoc, map_pure, seq_pure])
+
+export LawfulApplicative (seqLeft_eq seqRight_eq pure_seq map_pure seq_pure seq_assoc)
+
+attribute [simp] map_pure seq_pure
+
+@[simp] theorem pure_id_seq [Applicative f] [LawfulApplicative f] (x : f α) : pure id <*> x = x := by
+  simp [pure_seq]
+
+class LawfulMonad (m : Type u → Type v) [Monad m] extends LawfulApplicative m : Prop where
+  bind_pure_comp (f : α → β) (x : m α) : x >>= (fun a => pure (f a)) = f <$> x
+  bind_map       {α β : Type u} (f : m (α → β)) (x : m α) : f >>= (. <$> x) = f <*> x
+  pure_bind      (x : α) (f : α → m β) : pure x >>= f = f x
+  bind_assoc     (x : m α) (f : α → m β) (g : β → m γ) : x >>= f >>= g = x >>= fun x => f x >>= g
+  map_pure g x    := (by rw [← bind_pure_comp, pure_bind])
+  seq_pure g x    := (by rw [← bind_map]; simp [map_pure, bind_pure_comp])
+  seq_assoc x g h := (by simp [← bind_pure_comp, ← bind_map, bind_assoc, pure_bind])
+
+export LawfulMonad (bind_pure_comp bind_map pure_bind bind_assoc)
+attribute [simp] pure_bind bind_assoc
+
+@[simp] theorem bind_pure [Monad m] [LawfulMonad m] (x : m α) : x >>= pure = x := by
+  show x >>= (fun a => pure (id a)) = x
+  rw [bind_pure_comp, id_map]
+
+theorem map_eq_pure_bind [Monad m] [LawfulMonad m] (f : α → β) (x : m α) : f <$> x = x >>= fun a => pure (f a) := by
+  rw [← bind_pure_comp]
+
+theorem seq_eq_bind_map {α β : Type u} [Monad m] [LawfulMonad m] (f : m (α → β)) (x : m α) : f <*> x = f >>= (. <$> x) := by
+  rw [← bind_map]
+
+theorem bind_congr [Bind m] {x : m α} {f g : α → m β} (h : ∀ a, f a = g a) : x >>= f = x >>= g := by
+  simp [funext h]
+
+@[simp] theorem bind_pure_unit [Monad m] [LawfulMonad m] {x : m PUnit} : (x >>= fun _ => pure ⟨⟩) = x := by
+  rw [bind_pure]
+
+theorem map_congr [Functor m] {x : m α} {f g : α → β} (h : ∀ a, f a = g a) : (f <$> x : m β) = g <$> x := by
+  simp [funext h]
+
+theorem seq_eq_bind {α β : Type u} [Monad m] [LawfulMonad m] (mf : m (α → β)) (x : m α) : mf <*> x = mf >>= fun f => f <$> x := by
+  rw [bind_map]
+
+theorem seqRight_eq_bind [Monad m] [LawfulMonad m] (x : m α) (y : m β) : x *> y = x >>= fun _ => y := by
+  rw [seqRight_eq]
+  simp [map_eq_pure_bind, seq_eq_bind_map, const]
+
+theorem seqLeft_eq_bind [Monad m] [LawfulMonad m] (x : m α) (y : m β) : x <* y = x >>= fun a => y >>= fun _ => pure a := by
+  rw [seqLeft_eq]; simp [map_eq_pure_bind, seq_eq_bind_map]
+
+/--
+An alternative constructor for `LawfulMonad` which has more
+defaultable fields in the common case.
+-/
+theorem LawfulMonad.mk' (m : Type u → Type v) [Monad m]
+    (id_map : ∀ {α} (x : m α), id <$> x = x)
+    (pure_bind : ∀ {α β} (x : α) (f : α → m β), pure x >>= f = f x)
+    (bind_assoc : ∀ {α β γ} (x : m α) (f : α → m β) (g : β → m γ),
+      x >>= f >>= g = x >>= fun x => f x >>= g)
+    (map_const : ∀ {α β} (x : α) (y : m β),
+      Functor.mapConst x y = Function.const β x <$> y := by intros; rfl)
+    (seqLeft_eq : ∀ {α β} (x : m α) (y : m β),
+      x <* y = (x >>= fun a => y >>= fun _ => pure a) := by intros; rfl)
+    (seqRight_eq : ∀ {α β} (x : m α) (y : m β), x *> y = (x >>= fun _ => y) := by intros; rfl)
+    (bind_pure_comp : ∀ {α β} (f : α → β) (x : m α),
+      x >>= (fun y => pure (f y)) = f <$> x := by intros; rfl)
+    (bind_map : ∀ {α β} (f : m (α → β)) (x : m α), f >>= (. <$> x) = f <*> x := by intros; rfl)
+    : LawfulMonad m :=
+  have map_pure {α β} (g : α → β) (x : α) : g <$> (pure x : m α) = pure (g x) := by
+    rw [← bind_pure_comp]; simp [pure_bind]
+  { id_map, bind_pure_comp, bind_map, pure_bind, bind_assoc, map_pure,
+    comp_map := by simp [← bind_pure_comp, bind_assoc, pure_bind]
+    pure_seq := by intros; rw [← bind_map]; simp [pure_bind]
+    seq_pure := by intros; rw [← bind_map]; simp [map_pure, bind_pure_comp]
+    seq_assoc := by simp [← bind_pure_comp, ← bind_map, bind_assoc, pure_bind]
+    map_const := funext fun x => funext (map_const x)
+    seqLeft_eq := by simp [seqLeft_eq, ← bind_map, ← bind_pure_comp, pure_bind, bind_assoc]
+    seqRight_eq := fun x y => by
+      rw [seqRight_eq, ← bind_map, ← bind_pure_comp, bind_assoc]; simp [pure_bind, id_map] }
+
+/-! # Id -/
+
+namespace Id
+
+@[simp] theorem map_eq (x : Id α) (f : α → β) : f <$> x = f x := rfl
+@[simp] theorem bind_eq (x : Id α) (f : α → id β) : x >>= f = f x := rfl
+@[simp] theorem pure_eq (a : α) : (pure a : Id α) = a := rfl
+
+instance : LawfulMonad Id := by
+  refine' { .. } <;> intros <;> rfl
+
+end Id
+
+/-! # Option -/
+
+instance : LawfulMonad Option := LawfulMonad.mk'
+  (id_map := fun x => by cases x <;> rfl)
+  (pure_bind := fun x f => rfl)
+  (bind_assoc := fun x f g => by cases x <;> rfl)
+  (bind_pure_comp := fun f x => by cases x <;> rfl)
+
+instance : LawfulApplicative Option := inferInstance
+instance : LawfulFunctor Option := inferInstance

src/Init/Control/Lawful/Instances.lean

@@ -0,0 +1,248 @@
+/-
+Copyright (c) 2021 Microsoft Corporation. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Sebastian Ullrich, Leonardo de Moura, Mario Carneiro
+-/
+prelude
+import Init.Control.Lawful.Basic
+import Init.Control.Except
+import Init.Control.StateRef
+
+open Function
+
+/-! # ExceptT -/
+
+namespace ExceptT
+
+theorem ext [Monad m] {x y : ExceptT ε m α} (h : x.run = y.run) : x = y := by
+  simp [run] at h
+  assumption
+
+@[simp] theorem run_pure [Monad m] (x : α) : run (pure x : ExceptT ε m α) = pure (Except.ok x) := rfl
+
+@[simp] theorem run_lift  [Monad.{u, v} m] (x : m α) : run (ExceptT.lift x : ExceptT ε m α) = (Except.ok <$> x : m (Except ε α)) := rfl
+
+@[simp] theorem run_throw [Monad m] : run (throw e : ExceptT ε m β) = pure (Except.error e) := rfl
+
+@[simp] theorem run_bind_lift [Monad m] [LawfulMonad m] (x : m α) (f : α → ExceptT ε m β) : run (ExceptT.lift x >>= f : ExceptT ε m β) = x >>= fun a => run (f a) := by
+  simp[ExceptT.run, ExceptT.lift, bind, ExceptT.bind, ExceptT.mk, ExceptT.bindCont, map_eq_pure_bind]
+
+@[simp] theorem bind_throw [Monad m] [LawfulMonad m] (f : α → ExceptT ε m β) : (throw e >>= f) = throw e := by
+  simp [throw, throwThe, MonadExceptOf.throw, bind, ExceptT.bind, ExceptT.bindCont, ExceptT.mk]
+
+theorem run_bind [Monad m] (x : ExceptT ε m α)
+        : run (x >>= f : ExceptT ε m β)
+          =
+          run x >>= fun
+                     | Except.ok x => run (f x)
+                     | Except.error e => pure (Except.error e) :=
+  rfl
+
+@[simp] theorem lift_pure [Monad m] [LawfulMonad m] (a : α) : ExceptT.lift (pure a) = (pure a : ExceptT ε m α) := by
+  simp [ExceptT.lift, pure, ExceptT.pure]
+
+@[simp] theorem run_map [Monad m] [LawfulMonad m] (f : α → β) (x : ExceptT ε m α)
+    : (f <$> x).run = Except.map f <$> x.run := by
+  simp [Functor.map, ExceptT.map, map_eq_pure_bind]
+  apply bind_congr
+  intro a; cases a <;> simp [Except.map]
+
+protected theorem seq_eq {α β ε : Type u} [Monad m] (mf : ExceptT ε m (α → β)) (x : ExceptT ε m α) : mf <*> x = mf >>= fun f => f <$> x :=
+  rfl
+
+protected theorem bind_pure_comp [Monad m] [LawfulMonad m] (f : α → β) (x : ExceptT ε m α) : x >>= pure ∘ f = f <$> x := by
+  intros; rfl
+
+protected theorem seqLeft_eq {α β ε : Type u} {m : Type u → Type v} [Monad m] [LawfulMonad m] (x : ExceptT ε m α) (y : ExceptT ε m β) : x <* y = const β <$> x <*> y := by
+  show (x >>= fun a => y >>= fun _ => pure a) = (const (α := α) β <$> x) >>= fun f => f <$> y
+  rw [← ExceptT.bind_pure_comp]
+  apply ext
+  simp [run_bind]
+  apply bind_congr
+  intro
+  | Except.error _ => simp
+  | Except.ok _ =>
+    simp [map_eq_pure_bind]; apply bind_congr; intro b;
+    cases b <;> simp [comp, Except.map, const]
+
+protected theorem seqRight_eq [Monad m] [LawfulMonad m] (x : ExceptT ε m α) (y : ExceptT ε m β) : x *> y = const α id <$> x <*> y := by
+  show (x >>= fun _ => y) = (const α id <$> x) >>= fun f => f <$> y
+  rw [← ExceptT.bind_pure_comp]
+  apply ext
+  simp [run_bind]
+  apply bind_congr
+  intro a; cases a <;> simp
+
+instance [Monad m] [LawfulMonad m] : LawfulMonad (ExceptT ε m) where
+  id_map         := by intros; apply ext; simp
+  map_const      := by intros; rfl
+  seqLeft_eq     := ExceptT.seqLeft_eq
+  seqRight_eq    := ExceptT.seqRight_eq
+  pure_seq       := by intros; apply ext; simp [ExceptT.seq_eq, run_bind]
+  bind_pure_comp := ExceptT.bind_pure_comp
+  bind_map       := by intros; rfl
+  pure_bind      := by intros; apply ext; simp [run_bind]
+  bind_assoc     := by intros; apply ext; simp [run_bind]; apply bind_congr; intro a; cases a <;> simp
+
+end ExceptT
+
+/-! # Except -/
+
+instance : LawfulMonad (Except ε) := LawfulMonad.mk'
+  (id_map := fun x => by cases x <;> rfl)
+  (pure_bind := fun a f => rfl)
+  (bind_assoc := fun a f g => by cases a <;> rfl)
+
+instance : LawfulApplicative (Except ε) := inferInstance
+instance : LawfulFunctor (Except ε) := inferInstance
+
+/-! # ReaderT -/
+
+namespace ReaderT
+
+theorem ext {x y : ReaderT ρ m α} (h : ∀ ctx, x.run ctx = y.run ctx) : x = y := by
+  simp [run] at h
+  exact funext h
+
+@[simp] theorem run_pure [Monad m] (a : α) (ctx : ρ) : (pure a : ReaderT ρ m α).run ctx = pure a := rfl
+
+@[simp] theorem run_bind [Monad m] (x : ReaderT ρ m α) (f : α → ReaderT ρ m β) (ctx : ρ)
+    : (x >>= f).run ctx = x.run ctx >>= λ a => (f a).run ctx := rfl
+
+@[simp] theorem run_mapConst [Monad m] (a : α) (x : ReaderT ρ m β) (ctx : ρ)
+    : (Functor.mapConst a x).run ctx = Functor.mapConst a (x.run ctx) := rfl
+
+@[simp] theorem run_map [Monad m] (f : α → β) (x : ReaderT ρ m α) (ctx : ρ)
+    : (f <$> x).run ctx = f <$> x.run ctx := rfl
+
+@[simp] theorem run_monadLift [MonadLiftT n m] (x : n α) (ctx : ρ)
+    : (monadLift x : ReaderT ρ m α).run ctx = (monadLift x : m α) := rfl
+
+@[simp] theorem run_monadMap [MonadFunctor n m] (f : {β : Type u} → n β → n β) (x : ReaderT ρ m α) (ctx : ρ)
+    : (monadMap @f x : ReaderT ρ m α).run ctx = monadMap @f (x.run ctx) := rfl
+
+@[simp] theorem run_read [Monad m] (ctx : ρ) : (ReaderT.read : ReaderT ρ m ρ).run ctx = pure ctx := rfl
+
+@[simp] theorem run_seq {α β : Type u} [Monad m] (f : ReaderT ρ m (α → β)) (x : ReaderT ρ m α) (ctx : ρ)
+    : (f <*> x).run ctx = (f.run ctx <*> x.run ctx) := rfl
+
+@[simp] theorem run_seqRight [Monad m] (x : ReaderT ρ m α) (y : ReaderT ρ m β) (ctx : ρ)
+    : (x *> y).run ctx = (x.run ctx *> y.run ctx) := rfl
+
+@[simp] theorem run_seqLeft [Monad m] (x : ReaderT ρ m α) (y : ReaderT ρ m β) (ctx : ρ)
+    : (x <* y).run ctx = (x.run ctx <* y.run ctx) := rfl
+
+instance [Monad m] [LawfulFunctor m] : LawfulFunctor (ReaderT ρ m) where
+  id_map    := by intros; apply ext; simp
+  map_const := by intros; funext a b; apply ext; intros; simp [map_const]
+  comp_map  := by intros; apply ext; intros; simp [comp_map]
+
+instance [Monad m] [LawfulApplicative m] : LawfulApplicative (ReaderT ρ m) where
+  seqLeft_eq  := by intros; apply ext; intros; simp [seqLeft_eq]
+  seqRight_eq := by intros; apply ext; intros; simp [seqRight_eq]
+  pure_seq    := by intros; apply ext; intros; simp [pure_seq]
+  map_pure    := by intros; apply ext; intros; simp [map_pure]
+  seq_pure    := by intros; apply ext; intros; simp [seq_pure]
+  seq_assoc   := by intros; apply ext; intros; simp [seq_assoc]
+
+instance [Monad m] [LawfulMonad m] : LawfulMonad (ReaderT ρ m) where
+  bind_pure_comp := by intros; apply ext; intros; simp [LawfulMonad.bind_pure_comp]
+  bind_map       := by intros; apply ext; intros; simp [bind_map]
+  pure_bind      := by intros; apply ext; intros; simp
+  bind_assoc     := by intros; apply ext; intros; simp
+
+end ReaderT
+
+/-! # StateRefT -/
+
+instance [Monad m] [LawfulMonad m] : LawfulMonad (StateRefT' ω σ m) :=
+  inferInstanceAs (LawfulMonad (ReaderT (ST.Ref ω σ) m))
+
+/-! # StateT -/
+
+namespace StateT
+
+theorem ext {x y : StateT σ m α} (h : ∀ s, x.run s = y.run s) : x = y :=
+  funext h
+
+@[simp] theorem run'_eq [Monad m] (x : StateT σ m α) (s : σ) : run' x s = (·.1) <$> run x s :=
+  rfl
+
+@[simp] theorem run_pure [Monad m] (a : α) (s : σ) : (pure a : StateT σ m α).run s = pure (a, s) := rfl
+
+@[simp] theorem run_bind [Monad m] (x : StateT σ m α) (f : α → StateT σ m β) (s : σ)
+    : (x >>= f).run s = x.run s >>= λ p => (f p.1).run p.2 := by
+  simp [bind, StateT.bind, run]
+
+@[simp] theorem run_map {α β σ : Type u} [Monad m] [LawfulMonad m] (f : α → β) (x : StateT σ m α) (s : σ) : (f <$> x).run s = (fun (p : α × σ) => (f p.1, p.2)) <$> x.run s := by
+  simp [Functor.map, StateT.map, run, map_eq_pure_bind]
+
+@[simp] theorem run_get [Monad m] (s : σ)    : (get : StateT σ m σ).run s = pure (s, s) := rfl
+
+@[simp] theorem run_set [Monad m] (s s' : σ) : (set s' : StateT σ m PUnit).run s = pure (⟨⟩, s') := rfl
+
+@[simp] theorem run_modify [Monad m] (f : σ → σ) (s : σ) : (modify f : StateT σ m PUnit).run s = pure (⟨⟩, f s) := rfl
+
+@[simp] theorem run_modifyGet [Monad m] (f : σ → α × σ) (s : σ) : (modifyGet f : StateT σ m α).run s = pure ((f s).1, (f s).2) := by
+  simp [modifyGet, MonadStateOf.modifyGet, StateT.modifyGet, run]
+
+@[simp] theorem run_lift {α σ : Type u} [Monad m] (x : m α) (s : σ) : (StateT.lift x : StateT σ m α).run s = x >>= fun a => pure (a, s) := rfl
+
+@[simp] theorem run_bind_lift {α σ : Type u} [Monad m] [LawfulMonad m] (x : m α) (f : α → StateT σ m β) (s : σ) : (StateT.lift x >>= f).run s = x >>= fun a => (f a).run s := by
+  simp [StateT.lift, StateT.run, bind, StateT.bind]
+
+@[simp] theorem run_monadLift {α σ : Type u} [Monad m] [MonadLiftT n m] (x : n α) (s : σ) : (monadLift x : StateT σ m α).run s = (monadLift x : m α) >>= fun a => pure (a, s) := rfl
+
+@[simp] theorem run_monadMap [Monad m] [MonadFunctor n m] (f : {β : Type u} → n β → n β) (x : StateT σ m α) (s : σ)
+    : (monadMap @f x : StateT σ m α).run s = monadMap @f (x.run s) := rfl
+
+@[simp] theorem run_seq {α β σ : Type u} [Monad m] [LawfulMonad m] (f : StateT σ m (α → β)) (x : StateT σ m α) (s : σ) : (f <*> x).run s = (f.run s >>= fun fs => (fun (p : α × σ) => (fs.1 p.1, p.2)) <$> x.run fs.2) := by
+  show (f >>= fun g => g <$> x).run s = _
+  simp
+
+@[simp] theorem run_seqRight [Monad m] [LawfulMonad m] (x : StateT σ m α) (y : StateT σ m β) (s : σ) : (x *> y).run s = (x.run s >>= fun p => y.run p.2) := by
+  show (x >>= fun _ => y).run s = _
+  simp
+
+@[simp] theorem run_seqLeft {α β σ : Type u} [Monad m] [LawfulMonad m] (x : StateT σ m α) (y : StateT σ m β) (s : σ) : (x <* y).run s = (x.run s >>= fun p => y.run p.2 >>= fun p' => pure (p.1, p'.2)) := by
+  show (x >>= fun a => y >>= fun _ => pure a).run s = _
+  simp
+
+theorem seqRight_eq [Monad m] [LawfulMonad m] (x : StateT σ m α) (y : StateT σ m β) : x *> y = const α id <$> x <*> y := by
+  apply ext; intro s
+  simp [map_eq_pure_bind, const]
+  apply bind_congr; intro p; cases p
+  simp [Prod.eta]
+
+theorem seqLeft_eq [Monad m] [LawfulMonad m] (x : StateT σ m α) (y : StateT σ m β) : x <* y = const β <$> x <*> y := by
+  apply ext; intro s
+  simp [map_eq_pure_bind]
+
+instance [Monad m] [LawfulMonad m] : LawfulMonad (StateT σ m) where
+  id_map         := by intros; apply ext; intros; simp[Prod.eta]
+  map_const      := by intros; rfl
+  seqLeft_eq     := seqLeft_eq
+  seqRight_eq    := seqRight_eq
+  pure_seq       := by intros; apply ext; intros; simp
+  bind_pure_comp := by intros; apply ext; intros; simp; apply LawfulMonad.bind_pure_comp
+  bind_map       := by intros; rfl
+  pure_bind      := by intros; apply ext; intros; simp
+  bind_assoc     := by intros; apply ext; intros; simp
+
+end StateT
+
+/-! # EStateM -/
+
+instance : LawfulMonad (EStateM ε σ) := .mk'
+  (id_map := fun x => funext <| fun s => by
+    dsimp only [EStateM.instMonadEStateM, EStateM.map]
+    match x s with
+    | .ok _ _ => rfl
+    | .error _ _ => rfl)
+  (pure_bind := fun _ _ => rfl)
+  (bind_assoc := fun x _ _ => funext <| fun s => by
+    dsimp only [EStateM.instMonadEStateM, EStateM.bind]
+    match x s with
+    | .ok _ _ => rfl
+    | .error _ _ => rfl)
+  (map_const := fun _ _ => rfl)

src/Init/Control/StateCps.lean

@@ -4,7 +4,7 @@ Released under Apache 2.0 license as described in the file LICENSE.
 Authors: Leonardo de Moura
 -/
 prelude
-import Init.Control.Lawful
+import Init.Control.Lawful.Basic
 
 /-!
 The State monad transformer using CPS style.

src/Init/Conv.lean

@@ -6,7 +6,7 @@ Authors: Leonardo de Moura
 Notation for operators defined at Prelude.lean
 -/
 prelude
-import Init.NotationExtra
+import Init.Meta
 
 namespace Lean.Parser.Tactic.Conv
 
@@ -54,6 +54,10 @@ syntax (name := lhs) "lhs" : conv
 (In general, for an `n`-ary operator, it traverses into the last argument.) -/
 syntax (name := rhs) "rhs" : conv
 
+/-- Traverses into the function of a (unary) function application.
+For example, `| f a b` turns into `| f a`. (Use `arg 0` to traverse into `f`.)  -/
+syntax (name := «fun») "fun" : conv
+
 /-- Reduces the target to Weak Head Normal Form. This reduces definitions
 in "head position" until a constructor is exposed. For example, `List.map f [a, b, c]`
 weak head normalizes to `f a :: List.map f [b, c]`. -/
@@ -74,7 +78,8 @@ syntax (name := congr) "congr" : conv
 * `arg i` traverses into the `i`'th argument of the target. For example if the
   target is `f a b c d` then `arg 1` traverses to `a` and `arg 3` traverses to `c`.
 * `arg @i` is the same as `arg i` but it counts all arguments instead of just the
-  explicit arguments. -/
+  explicit arguments.
+* `arg 0` traverses into the function. If the target is `f a b c d`, `arg 0` traverses into `f`. -/
 syntax (name := arg) "arg " "@"? num : conv
 
 /-- `ext x` traverses into a binder (a `fun x => e` or `∀ x, e` expression)
@@ -151,7 +156,6 @@ match [a, b] with
 simplifies to `a`. -/
 syntax (name := simpMatch) "simp_match" : conv
 
-
 /-- Executes the given tactic block without converting `conv` goal into a regular goal. -/
 syntax (name := nestedTacticCore) "tactic'" " => " tacticSeq : conv
 
@@ -303,4 +307,7 @@ Basic forms:
 -- refer to the syntax category instead of this syntax
 syntax (name := conv) "conv" (" at " ident)? (" in " (occs)? term)? " => " convSeq : tactic
 
+/-- `norm_cast` tactic in `conv` mode. -/
+syntax (name := normCast) "norm_cast" : conv
+
 end Lean.Parser.Tactic.Conv

src/Init/Core.lean

@@ -17,7 +17,9 @@ universe u v w
 at the application site itself (by comparison to the `@[inline]` attribute,
 which applies to all applications of the function).
 -/
-def inline {α : Sort u} (a : α) : α := a
+@[simp] def inline {α : Sort u} (a : α) : α := a
+
+theorem id_def {α : Sort u} (a : α) : id a = a := rfl
 
 /--
 `flip f a b` is `f b a`. It is useful for "point-free" programming,
@@ -32,8 +34,32 @@ and `flip (·<·)` is the greater-than relation.
 
 @[simp] theorem Function.comp_apply {f : β → δ} {g : α → β} {x : α} : comp f g x = f (g x) := rfl
 
+theorem Function.comp_def {α β δ} (f : β → δ) (g : α → β) : f ∘ g = fun x => f (g x) := rfl
+
 attribute [simp] namedPattern
 
+/--
+`Empty.elim : Empty → C` says that a value of any type can be constructed from
+`Empty`. This can be thought of as a compiler-checked assertion that a code path is unreachable.
+
+This is a non-dependent variant of `Empty.rec`.
+-/
+@[macro_inline] def Empty.elim {C : Sort u} : Empty → C := Empty.rec
+
+/-- Decidable equality for Empty -/
+instance : DecidableEq Empty := fun a => a.elim
+
+/--
+`PEmpty.elim : Empty → C` says that a value of any type can be constructed from
+`PEmpty`. This can be thought of as a compiler-checked assertion that a code path is unreachable.
+
+This is a non-dependent variant of `PEmpty.rec`.
+-/
+@[macro_inline] def PEmpty.elim {C : Sort _} : PEmpty → C := fun a => nomatch a
+
+/-- Decidable equality for PEmpty -/
+instance : DecidableEq PEmpty := fun a => a.elim
+
 /--
   Thunks are "lazy" values that are evaluated when first accessed using `Thunk.get/map/bind`.
   The value is then stored and not recomputed for all further accesses. -/
@@ -78,6 +104,8 @@ instance thunkCoe : CoeTail α (Thunk α) where
 abbrev Eq.ndrecOn.{u1, u2} {α : Sort u2} {a : α} {motive : α → Sort u1} {b : α} (h : a = b) (m : motive a) : motive b :=
   Eq.ndrec m h
 
+/-! # definitions  -/
+
 /--
 If and only if, or logical bi-implication. `a ↔ b` means that `a` implies `b` and vice versa.
 By `propext`, this implies that `a` and `b` are equal and hence any expression involving `a`
@@ -126,6 +154,10 @@ inductive PSum (α : Sort u) (β : Sort v) where
 
 @[inherit_doc] infixr:30 " ⊕' " => PSum
 
+instance {α β} [Inhabited α] : Inhabited (PSum α β) := ⟨PSum.inl default⟩
+
+instance {α β} [Inhabited β] : Inhabited (PSum α β) := ⟨PSum.inr default⟩
+
 /--
 `Sigma β`, also denoted `Σ a : α, β a` or `(a : α) × β a`, is the type of dependent pairs
 whose first component is `a : α` and whose second component is `b : β a`
@@ -133,6 +165,7 @@ whose first component is `a : α` and whose second component is `b : β a`
 It is sometimes known as the dependent sum type, since it is the type level version
 of an indexed summation.
 -/
+@[pp_using_anonymous_constructor]
 structure Sigma {α : Type u} (β : α → Type v) where
   /-- Constructor for a dependent pair. If `a : α` and `b : β a` then `⟨a, b⟩ : Sigma β`.
   (This will usually require a type ascription to determine `β`
@@ -158,6 +191,7 @@ which can cause problems for universe level unification,
 because the equation `max 1 u v = ?u + 1` has no solution in level arithmetic.
 `PSigma` is usually only used in automation that constructs pairs of arbitrary types.
 -/
+@[pp_using_anonymous_constructor]
 structure PSigma {α : Sort u} (β : α → Sort v) where
   /-- Constructor for a dependent pair. If `a : α` and `b : β a` then `⟨a, b⟩ : PSigma β`.
   (This will usually require a type ascription to determine `β`
@@ -342,6 +376,70 @@ class HasEquiv (α : Sort u) where
 
 @[inherit_doc] infix:50 " ≈ "  => HasEquiv.Equiv
 
+/-! # set notation  -/
+
+/-- Notation type class for the subset relation `⊆`. -/
+class HasSubset (α : Type u) where
+  /-- Subset relation: `a ⊆ b`  -/
+  Subset : α → α → Prop
+export HasSubset (Subset)
+
+/-- Notation type class for the strict subset relation `⊂`. -/
+class HasSSubset (α : Type u) where
+  /-- Strict subset relation: `a ⊂ b`  -/
+  SSubset : α → α → Prop
+export HasSSubset (SSubset)
+
+/-- Superset relation: `a ⊇ b`  -/
+abbrev Superset [HasSubset α] (a b : α) := Subset b a
+
+/-- Strict superset relation: `a ⊃ b`  -/
+abbrev SSuperset [HasSSubset α] (a b : α) := SSubset b a
+
+/-- Notation type class for the union operation `∪`. -/
+class Union (α : Type u) where
+  /-- `a ∪ b` is the union of`a` and `b`. -/
+  union : α → α → α
+
+/-- Notation type class for the intersection operation `∩`. -/
+class Inter (α : Type u) where
+  /-- `a ∩ b` is the intersection of`a` and `b`. -/
+  inter : α → α → α
+
+/-- Notation type class for the set difference `\`. -/
+class SDiff (α : Type u) where
+  /--
+  `a \ b` is the set difference of `a` and `b`,
+  consisting of all elements in `a` that are not in `b`.
+  -/
+  sdiff : α → α → α
+
+/-- Subset relation: `a ⊆ b`  -/
+infix:50 " ⊆ " => Subset
+
+/-- Strict subset relation: `a ⊂ b`  -/
+infix:50 " ⊂ " => SSubset
+
+/-- Superset relation: `a ⊇ b`  -/
+infix:50 " ⊇ " => Superset
+
+/-- Strict superset relation: `a ⊃ b`  -/
+infix:50 " ⊃ " => SSuperset
+
+/-- `a ∪ b` is the union of`a` and `b`. -/
+infixl:65 " ∪ " => Union.union
+
+/-- `a ∩ b` is the intersection of`a` and `b`. -/
+infixl:70 " ∩ " => Inter.inter
+
+/--
+`a \ b` is the set difference of `a` and `b`,
+consisting of all elements in `a` that are not in `b`.
+-/
+infix:70 " \\ " => SDiff.sdiff
+
+/-! # collections  -/
+
 /-- `EmptyCollection α` is the typeclass which supports the notation `∅`, also written as `{}`. -/
 class EmptyCollection (α : Type u) where
   /-- `∅` or `{}` is the empty set or empty collection.
@@ -351,6 +449,36 @@ class EmptyCollection (α : Type u) where
 @[inherit_doc] notation "{" "}" => EmptyCollection.emptyCollection
 @[inherit_doc] notation "∅"     => EmptyCollection.emptyCollection
 
+/--
+Type class for the `insert` operation.
+Used to implement the `{ a, b, c }` syntax.
+-/
+class Insert (α : outParam <| Type u) (γ : Type v) where
+  /-- `insert x xs` inserts the element `x` into the collection `xs`. -/
+  insert : α → γ → γ
+export Insert (insert)
+
+/--
+Type class for the `singleton` operation.
+Used to implement the `{ a, b, c }` syntax.
+-/
+class Singleton (α : outParam <| Type u) (β : Type v) where
+  /-- `singleton x` is a collection with the single element `x` (notation: `{x}`). -/
+  singleton : α → β
+export Singleton (singleton)
+
+/-- `insert x ∅ = {x}` -/
+class IsLawfulSingleton (α : Type u) (β : Type v) [EmptyCollection β] [Insert α β] [Singleton α β] :
+    Prop where
+  /-- `insert x ∅ = {x}` -/
+  insert_emptyc_eq (x : α) : (insert x ∅ : β) = singleton x
+export IsLawfulSingleton (insert_emptyc_eq)
+
+/-- Type class used to implement the notation `{ a ∈ c | p a }` -/
+class Sep (α : outParam <| Type u) (γ : Type v) where
+  /-- Computes `{ a ∈ c | p a }`. -/
+  sep : (α → Prop) → γ → γ
+
 /--
 `Task α` is a primitive for asynchronous computation.
 It represents a computation that will resolve to a value of type `α`,
@@ -411,9 +539,10 @@ set_option linter.unusedVariables.funArgs false in
 be available and then calls `f` on the result.
 
 `prio`, if provided, is the priority of the task.
+If `sync` is set to true, `f` is executed on the current thread if `x` has already finished.
 -/
 @[noinline, extern "lean_task_map"]
-protected def map {α : Type u} {β : Type v} (f : α → β) (x : Task α) (prio := Priority.default) : Task β :=
+protected def map (f : α → β) (x : Task α) (prio := Priority.default) (sync := false) : Task β :=
   ⟨f x.get⟩
 
 set_option linter.unusedVariables.funArgs false in
@@ -424,9 +553,11 @@ for the value of `x` to be available and then calls `f` on the result,
 resulting in a new task which is then run for a result.
 
 `prio`, if provided, is the priority of the task.
+If `sync` is set to true, `f` is executed on the current thread if `x` has already finished.
 -/
 @[noinline, extern "lean_task_bind"]
-protected def bind {α : Type u} {β : Type v} (x : Task α) (f : α → Task β) (prio := Priority.default) : Task β :=
+protected def bind (x : Task α) (f : α → Task β) (prio := Priority.default) (sync := false) :
+    Task β :=
   ⟨(f x.get).get⟩
 
 end Task
@@ -522,9 +653,7 @@ theorem not_not_intro {p : Prop} (h : p) : ¬ ¬ p :=
   fun hn : ¬ p => hn h
 
 -- proof irrelevance is built in
-theorem proofIrrel {a : Prop} (h₁ h₂ : a) : h₁ = h₂ := rfl
-
-theorem id.def {α : Sort u} (a : α) : id a = a := rfl
+theorem proof_irrel {a : Prop} (h₁ h₂ : a) : h₁ = h₂ := rfl
 
 /--
 If `h : α = β` is a proof of type equality, then `h.mp : α → β` is the induced
@@ -550,7 +679,7 @@ You can prove theorems about the resulting element by induction on `h`, since
 theorem Eq.substr {α : Sort u} {p : α → Prop} {a b : α} (h₁ : b = a) (h₂ : p a) : p b :=
   h₁ ▸ h₂
 
-theorem cast_eq {α : Sort u} (h : α = α) (a : α) : cast h a = a :=
+@[simp] theorem cast_eq {α : Sort u} (h : α = α) (a : α) : cast h a = a :=
   rfl
 
 /--
@@ -572,8 +701,9 @@ theorem Ne.elim (h : a ≠ b) : a = b → False := h
 
 theorem Ne.irrefl (h : a ≠ a) : False := h rfl
 
-theorem Ne.symm (h : a ≠ b) : b ≠ a :=
-  fun h₁ => h (h₁.symm)
+theorem Ne.symm (h : a ≠ b) : b ≠ a := fun h₁ => h (h₁.symm)
+
+theorem ne_comm {α} {a b : α} : a ≠ b ↔ b ≠ a := ⟨Ne.symm, Ne.symm⟩
 
 theorem false_of_ne : a ≠ a → False := Ne.irrefl
 
@@ -585,8 +715,8 @@ theorem ne_true_of_not : ¬p → p ≠ True :=
     have : ¬True := h ▸ hnp
     this trivial
 
-theorem true_ne_false : ¬True = False :=
-  ne_false_of_self trivial
+theorem true_ne_false : ¬True = False := ne_false_of_self trivial
+theorem false_ne_true : False ≠ True := fun h => h.symm ▸ trivial
 
 end Ne
 
@@ -609,13 +739,16 @@ theorem beq_false_of_ne [BEq α] [LawfulBEq α] {a b : α} (h : a ≠ b) : (a ==
 section
 variable {α β φ : Sort u} {a a' : α} {b b' : β} {c : φ}
 
-theorem HEq.ndrec.{u1, u2} {α : Sort u2} {a : α} {motive : {β : Sort u2} → β → Sort u1} (m : motive a) {β : Sort u2} {b : β} (h : HEq a b) : motive b :=
+/-- Non-dependent recursor for `HEq` -/
+noncomputable def HEq.ndrec.{u1, u2} {α : Sort u2} {a : α} {motive : {β : Sort u2} → β → Sort u1} (m : motive a) {β : Sort u2} {b : β} (h : HEq a b) : motive b :=
   h.rec m
 
-theorem HEq.ndrecOn.{u1, u2} {α : Sort u2} {a : α} {motive : {β : Sort u2} → β → Sort u1} {β : Sort u2} {b : β} (h : HEq a b) (m : motive a) : motive b :=
+/-- `HEq.ndrec` variant -/
+noncomputable def HEq.ndrecOn.{u1, u2} {α : Sort u2} {a : α} {motive : {β : Sort u2} → β → Sort u1} {β : Sort u2} {b : β} (h : HEq a b) (m : motive a) : motive b :=
   h.rec m
 
-theorem HEq.elim {α : Sort u} {a : α} {p : α → Sort v} {b : α} (h₁ : HEq a b) (h₂ : p a) : p b :=
+/-- `HEq.ndrec` variant -/
+noncomputable def HEq.elim {α : Sort u} {a : α} {p : α → Sort v} {b : α} (h₁ : HEq a b) (h₂ : p a) : p b :=
   eq_of_heq h₁ ▸ h₂
 
 theorem HEq.subst {p : (T : Sort u) → T → Prop} (h₁ : HEq a b) (h₂ : p α a) : p β b :=
@@ -663,22 +796,31 @@ theorem Iff.refl (a : Prop) : a ↔ a :=
 protected theorem Iff.rfl {a : Prop} : a ↔ a :=
   Iff.refl a
 
+macro_rules | `(tactic| rfl) => `(tactic| exact Iff.rfl)
+
+theorem Iff.of_eq (h : a = b) : a ↔ b := h ▸ Iff.rfl
+
 theorem Iff.trans (h₁ : a ↔ b) (h₂ : b ↔ c) : a ↔ c :=
-  Iff.intro
-    (fun ha => Iff.mp h₂ (Iff.mp h₁ ha))
-    (fun hc => Iff.mpr h₁ (Iff.mpr h₂ hc))
+  Iff.intro (h₂.mp ∘ h₁.mp) (h₁.mpr ∘ h₂.mpr)
 
-theorem Iff.symm (h : a ↔ b) : b ↔ a :=
-  Iff.intro (Iff.mpr h) (Iff.mp h)
+-- This is needed for `calc` to work with `iff`.
+instance : Trans Iff Iff Iff where
+  trans := Iff.trans
 
-theorem Iff.comm : (a ↔ b) ↔ (b ↔ a) :=
-  Iff.intro Iff.symm Iff.symm
+theorem Eq.comm {a b : α} : a = b ↔ b = a := Iff.intro Eq.symm Eq.symm
+theorem eq_comm {a b : α} : a = b ↔ b = a := Eq.comm
 
-theorem Iff.of_eq (h : a = b) : a ↔ b :=
-  h ▸ Iff.refl _
+theorem Iff.symm (h : a ↔ b) : b ↔ a := Iff.intro h.mpr h.mp
+theorem Iff.comm: (a ↔ b) ↔ (b ↔ a) := Iff.intro Iff.symm Iff.symm
+theorem iff_comm : (a ↔ b) ↔ (b ↔ a) := Iff.comm
 
-theorem And.comm : a ∧ b ↔ b ∧ a := by
-  constructor <;> intro ⟨h₁, h₂⟩ <;> exact ⟨h₂, h₁⟩
+theorem And.symm : a ∧ b → b ∧ a := fun ⟨ha, hb⟩ => ⟨hb, ha⟩
+theorem And.comm : a ∧ b ↔ b ∧ a := Iff.intro And.symm And.symm
+theorem and_comm : a ∧ b ↔ b ∧ a := And.comm
+
+theorem Or.symm : a ∨ b → b ∨ a := .rec .inr .inl
+theorem Or.comm : a ∨ b ↔ b ∨ a := Iff.intro Or.symm Or.symm
+theorem or_comm : a ∨ b ↔ b ∨ a := Or.comm
 
 /-! # Exists -/
 
@@ -878,8 +1020,13 @@ protected theorem Subsingleton.helim {α β : Sort u} [h₁ : Subsingleton α] (
   apply heq_of_eq
   apply Subsingleton.elim
 
-instance (p : Prop) : Subsingleton p :=
-  ⟨fun a b => proofIrrel a b⟩
+instance (p : Prop) : Subsingleton p := ⟨fun a b => proof_irrel a b⟩
+
+instance : Subsingleton Empty  := ⟨(·.elim)⟩
+instance : Subsingleton PEmpty := ⟨(·.elim)⟩
+
+instance [Subsingleton α] [Subsingleton β] : Subsingleton (α × β) :=
+  ⟨fun {..} {..} => by congr <;> apply Subsingleton.elim⟩
 
 instance (p : Prop) : Subsingleton (Decidable p) :=
   Subsingleton.intro fun
@@ -890,6 +1037,9 @@ instance (p : Prop) : Subsingleton (Decidable p) :=
       | isTrue t₂  => absurd t₂ f₁
       | isFalse _  => rfl
 
+example [Subsingleton α] (p : α → Prop) : Subsingleton (Subtype p) :=
+  ⟨fun ⟨x, _⟩ ⟨y, _⟩ => by congr; exact Subsingleton.elim x y⟩
+
 theorem recSubsingleton
      {p : Prop} [h : Decidable p]
      {h₁ : p → Sort u}
@@ -1169,12 +1319,117 @@ gen_injective_theorems% Lean.Syntax
 @[simp] theorem beq_iff_eq [BEq α] [LawfulBEq α] (a b : α) : a == b ↔ a = b :=
   ⟨eq_of_beq, by intro h; subst h; exact LawfulBEq.rfl⟩
 
-/-! # Quotients -/
+/-! # Prop lemmas -/
+
+/-- *Ex falso* for negation: from `¬a` and `a` anything follows. This is the same as `absurd` with
+the arguments flipped, but it is in the `Not` namespace so that projection notation can be used. -/
+def Not.elim {α : Sort _} (H1 : ¬a) (H2 : a) : α := absurd H2 H1
+
+/-- Non-dependent eliminator for `And`. -/
+abbrev And.elim (f : a → b → α) (h : a ∧ b) : α := f h.left h.right
+
+/-- Non-dependent eliminator for `Iff`. -/
+def Iff.elim (f : (a → b) → (b → a) → α) (h : a ↔ b) : α := f h.mp h.mpr
 
 /-- Iff can now be used to do substitutions in a calculation -/
 theorem Iff.subst {a b : Prop} {p : Prop → Prop} (h₁ : a ↔ b) (h₂ : p a) : p b :=
   Eq.subst (propext h₁) h₂
 
+theorem Not.intro {a : Prop} (h : a → False) : ¬a := h
+
+theorem Not.imp {a b : Prop} (H2 : ¬b) (H1 : a → b) : ¬a := mt H1 H2
+
+theorem not_congr (h : a ↔ b) : ¬a ↔ ¬b := ⟨mt h.2, mt h.1⟩
+
+theorem not_not_not : ¬¬¬a ↔ ¬a := ⟨mt not_not_intro, not_not_intro⟩
+
+theorem iff_of_true (ha : a) (hb : b) : a ↔ b := Iff.intro (fun _ => hb) (fun _ => ha)
+theorem iff_of_false (ha : ¬a) (hb : ¬b) : a ↔ b := Iff.intro ha.elim hb.elim
+
+theorem iff_true_left  (ha : a) : (a ↔ b) ↔ b := Iff.intro (·.mp ha) (iff_of_true ha)
+theorem iff_true_right (ha : a) : (b ↔ a) ↔ b := Iff.comm.trans (iff_true_left ha)
+
+theorem iff_false_left  (ha : ¬a) : (a ↔ b) ↔ ¬b := Iff.intro (mt ·.mpr ha) (iff_of_false ha)
+theorem iff_false_right (ha : ¬a) : (b ↔ a) ↔ ¬b := Iff.comm.trans (iff_false_left ha)
+
+theorem of_iff_true    (h : a ↔ True) : a := h.mpr trivial
+theorem iff_true_intro (h : a) : a ↔ True := iff_of_true h trivial
+
+theorem not_of_iff_false : (p ↔ False) → ¬p := Iff.mp
+theorem iff_false_intro (h : ¬a) : a ↔ False := iff_of_false h id
+
+theorem not_iff_false_intro (h : a) : ¬a ↔ False := iff_false_intro (not_not_intro h)
+theorem not_true : (¬True) ↔ False := iff_false_intro (not_not_intro trivial)
+
+theorem not_false_iff : (¬False) ↔ True := iff_true_intro not_false
+
+theorem Eq.to_iff : a = b → (a ↔ b) := Iff.of_eq
+theorem iff_of_eq : a = b → (a ↔ b) := Iff.of_eq
+theorem neq_of_not_iff : ¬(a ↔ b) → a ≠ b := mt Iff.of_eq
+
+theorem iff_iff_eq : (a ↔ b) ↔ a = b := Iff.intro propext Iff.of_eq
+@[simp] theorem eq_iff_iff : (a = b) ↔ (a ↔ b) := iff_iff_eq.symm
+
+theorem eq_self_iff_true (a : α)  : a = a ↔ True  := iff_true_intro rfl
+theorem ne_self_iff_false (a : α) : a ≠ a ↔ False := not_iff_false_intro rfl
+
+theorem false_of_true_iff_false (h : True ↔ False) : False := h.mp trivial
+theorem false_of_true_eq_false  (h : True = False) : False := false_of_true_iff_false (Iff.of_eq h)
+
+theorem true_eq_false_of_false : False → (True = False) := False.elim
+
+theorem iff_def  : (a ↔ b) ↔ (a → b) ∧ (b → a) := iff_iff_implies_and_implies a b
+theorem iff_def' : (a ↔ b) ↔ (b → a) ∧ (a → b) := Iff.trans iff_def And.comm
+
+theorem true_iff_false : (True ↔ False) ↔ False := iff_false_intro (·.mp  True.intro)
+theorem false_iff_true : (False ↔ True) ↔ False := iff_false_intro (·.mpr True.intro)
+
+theorem iff_not_self : ¬(a ↔ ¬a) | H => let f h := H.1 h h; f (H.2 f)
+theorem heq_self_iff_true (a : α) : HEq a a ↔ True := iff_true_intro HEq.rfl
+
+/-! ## implies -/
+
+theorem not_not_of_not_imp : ¬(a → b) → ¬¬a := mt Not.elim
+
+theorem not_of_not_imp {a : Prop} : ¬(a → b) → ¬b := mt fun h _ => h
+
+@[simp] theorem imp_not_self : (a → ¬a) ↔ ¬a := Iff.intro (fun h ha => h ha ha) (fun h _ => h)
+
+theorem imp_intro {α β : Prop} (h : α) : β → α := fun _ => h
+
+theorem imp_imp_imp {a b c d : Prop} (h₀ : c → a) (h₁ : b → d) : (a → b) → (c → d) := (h₁ ∘ · ∘ h₀)
+
+theorem imp_iff_right {a : Prop} (ha : a) : (a → b) ↔ b := Iff.intro (· ha) (fun a _ => a)
+
+-- This is not marked `@[simp]` because we have `implies_true : (α → True) = True`
+theorem imp_true_iff (α : Sort u) : (α → True) ↔ True := iff_true_intro (fun _ => trivial)
+
+theorem false_imp_iff (a : Prop) : (False → a) ↔ True := iff_true_intro False.elim
+
+theorem true_imp_iff (α : Prop) : (True → α) ↔ α := imp_iff_right True.intro
+
+@[simp high] theorem imp_self : (a → a) ↔ True := iff_true_intro id
+
+@[simp] theorem imp_false : (a → False) ↔ ¬a := Iff.rfl
+
+theorem imp.swap : (a → b → c) ↔ (b → a → c) := Iff.intro flip flip
+
+theorem imp_not_comm : (a → ¬b) ↔ (b → ¬a) := imp.swap
+
+theorem imp_congr_left (h : a ↔ b) : (a → c) ↔ (b → c) := Iff.intro (· ∘ h.mpr) (· ∘ h.mp)
+
+theorem imp_congr_right (h : a → (b ↔ c)) : (a → b) ↔ (a → c) :=
+  Iff.intro (fun hab ha => (h ha).mp (hab ha)) (fun hcd ha => (h ha).mpr (hcd ha))
+
+theorem imp_congr_ctx (h₁ : a ↔ c) (h₂ : c → (b ↔ d)) : (a → b) ↔ (c → d) :=
+  Iff.trans (imp_congr_left h₁) (imp_congr_right h₂)
+
+theorem imp_congr (h₁ : a ↔ c) (h₂ : b ↔ d) : (a → b) ↔ (c → d) := imp_congr_ctx h₁ fun _ => h₂
+
+theorem imp_iff_not (hb : ¬b) : a → b ↔ ¬a := imp_congr_right fun _ => iff_false_intro hb
+
+/-! # Quotients -/
+
 namespace Quot
 /--
 The **quotient axiom**, or at least the nontrivial part of the quotient
@@ -1341,7 +1596,7 @@ protected def mk' {α : Sort u} [s : Setoid α] (a : α) : Quotient s :=
 The analogue of `Quot.sound`: If `a` and `b` are related by the equivalence relation,
 then they have equal equivalence classes.
 -/
-def sound {α : Sort u} {s : Setoid α} {a b : α} : a ≈ b → Quotient.mk s a = Quotient.mk s b :=
+theorem sound {α : Sort u} {s : Setoid α} {a b : α} : a ≈ b → Quotient.mk s a = Quotient.mk s b :=
   Quot.sound
 
 /--
@@ -1680,40 +1935,104 @@ So, you are mainly losing the capability of type checking your development using
 -/
 axiom ofReduceNat (a b : Nat) (h : reduceNat a = b) : a = b
 
+end Lean
+
+@[simp] theorem ge_iff_le [LE α] {x y : α} : x ≥ y ↔ y ≤ x := Iff.rfl
+
+@[simp] theorem gt_iff_lt [LT α] {x y : α} : x > y ↔ y < x := Iff.rfl
+
+theorem le_of_eq_of_le {a b c : α} [LE α] (h₁ : a = b) (h₂ : b ≤ c) : a ≤ c := h₁ ▸ h₂
+
+theorem le_of_le_of_eq {a b c : α} [LE α] (h₁ : a ≤ b) (h₂ : b = c) : a ≤ c := h₂ ▸ h₁
+
+theorem lt_of_eq_of_lt {a b c : α} [LT α] (h₁ : a = b) (h₂ : b < c) : a < c := h₁ ▸ h₂
+
+theorem lt_of_lt_of_eq {a b c : α} [LT α] (h₁ : a < b) (h₂ : b = c) : a < c := h₂ ▸ h₁
+
+namespace Std
+variable {α : Sort u}
+
 /--
-`IsAssociative op` says that `op` is an associative operation,
-i.e. `(a ∘ b) ∘ c = a ∘ (b ∘ c)`. It is used by the `ac_rfl` tactic.
+`Associative op` indicates `op` is an associative operation,
+i.e. `(a ∘ b) ∘ c = a ∘ (b ∘ c)`.
 -/
-class IsAssociative {α : Sort u} (op : α → α → α) where
+class Associative (op : α → α → α) : Prop where
   /-- An associative operation satisfies `(a ∘ b) ∘ c = a ∘ (b ∘ c)`. -/
   assoc : (a b c : α) → op (op a b) c = op a (op b c)
 
 /--
-`IsCommutative op` says that `op` is a commutative operation,
-i.e. `a ∘ b = b ∘ a`. It is used by the `ac_rfl` tactic.
+`Commutative op` says that `op` is a commutative operation,
+i.e. `a ∘ b = b ∘ a`.
 -/
-class IsCommutative {α : Sort u} (op : α → α → α) where
+class Commutative (op : α → α → α) : Prop where
   /-- A commutative operation satisfies `a ∘ b = b ∘ a`. -/
   comm : (a b : α) → op a b = op b a
 
 /--
-`IsIdempotent op` says that `op` is an idempotent operation,
-i.e. `a ∘ a = a`. It is used by the `ac_rfl` tactic
-(which also simplifies up to idempotence when available).
+`IdempotentOp op` indicates `op` is an idempotent binary operation.
+i.e. `a ∘ a = a`.
 -/
-class IsIdempotent {α : Sort u} (op : α → α → α) where
+class IdempotentOp (op : α → α → α) : Prop where
   /-- An idempotent operation satisfies `a ∘ a = a`. -/
   idempotent : (x : α) → op x x = x
 
 /--
-`IsNeutral op e` says that `e` is a neutral operation for `op`,
-i.e. `a ∘ e = a = e ∘ a`. It is used by the `ac_rfl` tactic
-(which also simplifies neutral elements when available).
--/
-class IsNeutral {α : Sort u} (op : α → α → α) (neutral : α) where
-  /-- A neutral element can be cancelled on the left: `e ∘ a = a`. -/
-  left_neutral : (a : α) → op neutral a = a
-  /-- A neutral element can be cancelled on the right: `a ∘ e = a`. -/
-  right_neutral : (a : α) → op a neutral = a
+`LeftIdentify op o` indicates `o` is a left identity of `op`.
 
-end Lean
+This class does not require a proof that `o` is an identity, and
+is used primarily for infering the identity using class resoluton.
+-/
+class LeftIdentity (op : α → β → β) (o : outParam α) : Prop
+
+/--
+`LawfulLeftIdentify op o` indicates `o` is a verified left identity of
+`op`.
+-/
+class LawfulLeftIdentity (op : α → β → β) (o : outParam α) extends LeftIdentity op o : Prop where
+  /-- Left identity `o` is an identity. -/
+  left_id : ∀ a, op o a = a
+
+/--
+`RightIdentify op o` indicates `o` is a right identity `o` of `op`.
+
+This class does not require a proof that `o` is an identity, and is used
+primarily for infering the identity using class resoluton.
+-/
+class RightIdentity (op : α → β → α) (o : outParam β) : Prop
+
+/--
+`LawfulRightIdentify op o` indicates `o` is a verified right identity of
+`op`.
+-/
+class LawfulRightIdentity (op : α → β → α) (o : outParam β) extends RightIdentity op o : Prop where
+  /-- Right identity `o` is an identity. -/
+  right_id : ∀ a, op a o = a
+
+/--
+`Identity op o` indicates `o` is a left and right identity of `op`.
+
+This class does not require a proof that `o` is an identity, and is used
+primarily for infering the identity using class resoluton.
+-/
+class Identity (op : α → α → α) (o : outParam α) extends LeftIdentity op o, RightIdentity op o : Prop
+
+/--
+`LawfulIdentity op o` indicates `o` is a verified left and right
+identity of `op`.
+-/
+class LawfulIdentity (op : α → α → α) (o : outParam α) extends Identity op o, LawfulLeftIdentity op o, LawfulRightIdentity op o : Prop
+
+/--
+`LawfulCommIdentity` can simplify defining instances of `LawfulIdentity`
+on commutative functions by requiring only a left or right identity
+proof.
+
+This class is intended for simplifying defining instances of
+`LawfulIdentity` and functions needed commutative operations with
+identity should just add a `LawfulIdentity` constraint.
+-/
+class LawfulCommIdentity (op : α → α → α) (o : outParam α) [hc : Commutative op] extends LawfulIdentity op o : Prop where
+  left_id a := Eq.trans (hc.comm o a) (right_id a)
+  right_id a := Eq.trans (hc.comm a o) (left_id a)
+
+end Std

src/Init/Data.lean

@@ -6,6 +6,9 @@ Authors: Leonardo de Moura
 prelude
 import Init.Data.Basic
 import Init.Data.Nat
+import Init.Data.Bool
+import Init.Data.BitVec
+import Init.Data.Cast
 import Init.Data.Char
 import Init.Data.String
 import Init.Data.List
@@ -29,3 +32,5 @@ import Init.Data.Prod
 import Init.Data.AC
 import Init.Data.Queue
 import Init.Data.Channel
+import Init.Data.Cast
+import Init.Data.Sum

src/Init/Data/AC.lean

@@ -14,15 +14,17 @@ inductive Expr
   | op (lhs rhs : Expr)
   deriving Inhabited, Repr, BEq
 
+open Std
+
 structure Variable {α : Sort u} (op : α → α → α) : Type u where
   value : α
-  neutral : Option $ IsNeutral op value
+  neutral : Option $ PLift (LawfulIdentity op value)
 
 structure Context (α : Sort u) where
   op : α → α → α
-  assoc : IsAssociative op
-  comm : Option $ IsCommutative op
-  idem : Option $ IsIdempotent op
+  assoc : Associative op
+  comm : Option $ PLift $ Commutative op
+  idem : Option $ PLift $ IdempotentOp op
   vars : List (Variable op)
   arbitrary : α
 
@@ -104,7 +106,7 @@ def norm [info : ContextInformation α] (ctx : α) (e : Expr) : List Nat :=
   let xs := if info.isComm ctx then sort xs else xs
   if info.isIdem ctx then mergeIdem xs else xs
 
-theorem List.two_step_induction
+noncomputable def List.two_step_induction
   {motive : List Nat → Sort u}
   (l : List Nat)
   (empty : motive [])
@@ -128,7 +130,14 @@ theorem Context.mergeIdem_head2 (h : x ≠ y) : mergeIdem (x :: y :: ys) = x ::
   simp [mergeIdem, mergeIdem.loop, h]
 
 theorem Context.evalList_mergeIdem (ctx : Context α) (h : ContextInformation.isIdem ctx) (e : List Nat) : evalList α ctx (mergeIdem e) = evalList α ctx e := by
-  have h : IsIdempotent ctx.op := by simp [ContextInformation.isIdem, Option.isSome] at h; cases h₂ : ctx.idem <;> simp [h₂] at h; assumption
+  have h : IdempotentOp ctx.op := by
+    simp [ContextInformation.isIdem, Option.isSome] at h;
+    match h₂ : ctx.idem with
+    | none =>
+      simp [h₂] at h
+    | some val =>
+      simp [h₂] at h
+      exact val.down
   induction e using List.two_step_induction with
   | empty => rfl
   | single => rfl
@@ -141,18 +150,18 @@ theorem Context.evalList_mergeIdem (ctx : Context α) (h : ContextInformation.is
       rfl
     | cons z zs =>
       by_cases h₂ : x = y
-      case inl =>
+      case pos =>
         rw [h₂, mergeIdem_head, ih]
         simp [evalList, ←ctx.assoc.1, h.1, EvalInformation.evalOp]
-      case inr =>
+      case neg =>
         rw [mergeIdem_head2]
         by_cases h₃ : y = z
-        case inl =>
+        case pos =>
           simp [mergeIdem_head, h₃, evalList]
           cases h₄ : mergeIdem (z :: zs) with
           | nil => apply absurd h₄; apply mergeIdem_nonEmpty; simp
           | cons u us => simp_all [mergeIdem, mergeIdem.loop, evalList]
-        case inr =>
+        case neg =>
           simp [mergeIdem_head2, h₃, evalList] at *
           rw [ih]
         assumption
@@ -169,7 +178,7 @@ theorem Context.sort_loop_nonEmpty (xs : List Nat) (h : xs ≠ []) : sort.loop x
 
 theorem Context.evalList_insert
   (ctx : Context α)
-  (h : IsCommutative ctx.op)
+  (h : Commutative ctx.op)
   (x : Nat)
   (xs : List Nat)
   : evalList α ctx (insert x xs) = evalList α ctx (x::xs) := by
@@ -190,7 +199,7 @@ theorem Context.evalList_insert
 
 theorem Context.evalList_sort_congr
   (ctx : Context α)
-  (h : IsCommutative ctx.op)
+  (h : Commutative ctx.op)
   (h₂ : evalList α ctx a = evalList α ctx b)
   (h₃ : a ≠ [])
   (h₄ : b ≠ [])
@@ -209,7 +218,7 @@ theorem Context.evalList_sort_congr
 
 theorem Context.evalList_sort_loop_swap
   (ctx : Context α)
-  (h : IsCommutative ctx.op)
+  (h : Commutative ctx.op)
   (xs ys : List Nat)
   : evalList α ctx (sort.loop xs (y::ys)) = evalList α ctx (sort.loop (y::xs) ys) := by
   induction ys generalizing y xs with
@@ -224,7 +233,7 @@ theorem Context.evalList_sort_loop_swap
 
 theorem Context.evalList_sort_cons
   (ctx : Context α)
-  (h : IsCommutative ctx.op)
+  (h : Commutative ctx.op)
   (x : Nat)
   (xs : List Nat)
   : evalList α ctx (sort (x :: xs)) = evalList α ctx (x :: sort xs) := by
@@ -247,7 +256,14 @@ theorem Context.evalList_sort_cons
     all_goals simp [insert_nonEmpty]
 
 theorem Context.evalList_sort (ctx : Context α) (h : ContextInformation.isComm ctx) (e : List Nat) : evalList α ctx (sort e) = evalList α ctx e := by
-  have h : IsCommutative ctx.op := by simp [ContextInformation.isComm, Option.isSome] at h; cases h₂ : ctx.comm <;> simp [h₂] at h; assumption
+  have h : Commutative ctx.op := by
+    simp [ContextInformation.isComm, Option.isSome] at h
+    match h₂ : ctx.comm with
+    | none =>
+      simp only [h₂] at h
+    | some val =>
+      simp [h₂] at h
+      exact val.down
   induction e using List.two_step_induction with
   | empty => rfl
   | single => rfl
@@ -269,10 +285,12 @@ theorem Context.toList_nonEmpty (e : Expr) : e.toList ≠ [] := by
 theorem Context.unwrap_isNeutral
   {ctx : Context α}
   {x : Nat}
-  : ContextInformation.isNeutral ctx x = true → IsNeutral (EvalInformation.evalOp ctx) (EvalInformation.evalVar (β := α) ctx x) := by
+  : ContextInformation.isNeutral ctx x = true → LawfulIdentity (EvalInformation.evalOp ctx) (EvalInformation.evalVar (β := α) ctx x) := by
   simp [ContextInformation.isNeutral, Option.isSome, EvalInformation.evalOp, EvalInformation.evalVar]
   match (var ctx x).neutral with
-  | some hn => intro; assumption
+  | some hn =>
+    intro
+    exact hn.down
   | none => intro; contradiction
 
 theorem Context.evalList_removeNeutrals (ctx : Context α) (e : List Nat) : evalList α ctx (removeNeutrals ctx e) = evalList α ctx e := by
@@ -283,10 +301,12 @@ theorem Context.evalList_removeNeutrals (ctx : Context α) (e : List Nat) : eval
     case h_1 => rfl
     case h_2 h => split at h <;> simp_all
   | step x y ys ih =>
-    cases h₁ : ContextInformation.isNeutral ctx x <;> cases h₂ : ContextInformation.isNeutral ctx y <;> cases h₃ : removeNeutrals.loop ctx ys
+    cases h₁ : ContextInformation.isNeutral ctx x <;>
+    cases h₂ : ContextInformation.isNeutral ctx y <;>
+    cases h₃ : removeNeutrals.loop ctx ys
     <;> simp [removeNeutrals, removeNeutrals.loop, h₁, h₂, h₃, evalList, ←ih]
-    <;> (try simp [unwrap_isNeutral h₂ |>.2])
-    <;> (try simp [unwrap_isNeutral h₁ |>.1])
+    <;> (try simp [unwrap_isNeutral h₂ |>.right_id])
+    <;> (try simp [unwrap_isNeutral h₁ |>.left_id])
 
 theorem Context.evalList_append
   (ctx : Context α)

src/Init/Data/Array.lean

@@ -11,3 +11,4 @@ import Init.Data.Array.InsertionSort
 import Init.Data.Array.DecidableEq
 import Init.Data.Array.Mem
 import Init.Data.Array.BasicAux
+import Init.Data.Array.Lemmas

src/Init/Data/Array/Basic.lean

@@ -21,6 +21,21 @@ def mkArray {α : Type u} (n : Nat) (v : α) : Array α := {
   data := List.replicate n v
 }
 
+/--
+`ofFn f` with `f : Fin n → α` returns the list whose ith element is `f i`.
+```
+ofFn f = #[f 0, f 1, ... , f(n - 1)]
+``` -/
+def ofFn {n} (f : Fin n → α) : Array α := go 0 (mkEmpty n) where
+  /-- Auxiliary for `ofFn`. `ofFn.go f i acc = acc ++ #[f i, ..., f(n - 1)]` -/
+  go (i : Nat) (acc : Array α) : Array α :=
+    if h : i < n then go (i+1) (acc.push (f ⟨i, h⟩)) else acc
+termination_by n - i
+
+/-- The array `#[0, 1, ..., n - 1]`. -/
+def range (n : Nat) : Array Nat :=
+  n.fold (flip Array.push) (mkEmpty n)
+
 @[simp] theorem size_mkArray (n : Nat) (v : α) : (mkArray n v).size = n :=
   List.length_replicate ..
 
@@ -71,6 +86,12 @@ abbrev getLit {α : Type u} {n : Nat} (a : Array α) (i : Nat) (h₁ : a.size =
 def uset (a : Array α) (i : USize) (v : α) (h : i.toNat < a.size) : Array α :=
   a.set ⟨i.toNat, h⟩ v
 
+/--
+Swaps two entries in an array.
+
+This will perform the update destructively provided that `a` has a reference
+count of 1 when called.
+-/
 @[extern "lean_array_fswap"]
 def swap (a : Array α) (i j : @& Fin a.size) : Array α :=
   let v₁ := a.get i
@@ -78,12 +99,18 @@ def swap (a : Array α) (i j : @& Fin a.size) : Array α :=
   let a'  := a.set i v₂
   a'.set (size_set a i v₂ ▸ j) v₁
 
+/--
+Swaps two entries in an array, or panics if either index is out of bounds.
+
+This will perform the update destructively provided that `a` has a reference
+count of 1 when called.
+-/
 @[extern "lean_array_swap"]
 def swap! (a : Array α) (i j : @& Nat) : Array α :=
   if h₁ : i < a.size then
   if h₂ : j < a.size then swap a ⟨i, h₁⟩ ⟨j, h₂⟩
-  else panic! "index out of bounds"
-  else panic! "index out of bounds"
+  else a
+  else a
 
 @[inline] def swapAt (a : Array α) (i : Fin a.size) (v : α) : α × Array α :=
   let e := a.get i
@@ -276,8 +303,8 @@ def mapM {α : Type u} {β : Type v} {m : Type v → Type w} [Monad m] (f : α
       map (i+1) (r.push (← f as[i]))
     else
       pure r
+  termination_by as.size - i
   map 0 (mkEmpty as.size)
-termination_by map => as.size - i
 
 @[inline]
 def mapIdxM {α : Type u} {β : Type v} {m : Type v → Type w} [Monad m] (as : Array α) (f : Fin as.size → α → m β) : m (Array β) :=
@@ -348,12 +375,12 @@ def anyM {α : Type u} {m : Type → Type w} [Monad m] (p : α → m Bool) (as :
           loop (j+1)
       else
         pure false
+      termination_by stop - j
     loop start
   if h : stop ≤ as.size then
     any stop h
   else
     any as.size (Nat.le_refl _)
-termination_by loop i j => stop - j
 
 @[inline]
 def allM {α : Type u} {m : Type → Type w} [Monad m] (p : α → m Bool) (as : Array α) (start := 0) (stop := as.size) : m Bool :=
@@ -401,6 +428,10 @@ def map {α : Type u} {β : Type v} (f : α → β) (as : Array α) : Array β :
 def mapIdx {α : Type u} {β : Type v} (as : Array α) (f : Fin as.size → α → β) : Array β :=
   Id.run <| as.mapIdxM f
 
+/-- Turns `#[a, b]` into `#[(a, 0), (b, 1)]`. -/
+def zipWithIndex (arr : Array α) : Array (α × Nat) :=
+  arr.mapIdx fun i a => (a, i)
+
 @[inline]
 def find? {α : Type} (as : Array α) (p : α → Bool) : Option α :=
   Id.run <| as.findM? p
@@ -425,24 +456,12 @@ def findRev? {α : Type} (as : Array α) (p : α → Bool) : Option α :=
 
 @[inline]
 def findIdx? {α : Type u} (as : Array α) (p : α → Bool) : Option Nat :=
-  let rec loop (i : Nat) (j : Nat) (inv : i + j = as.size) : Option Nat :=
-    if hlt : j < as.size then
-      match i, inv with
-      | 0, inv => by
-        apply False.elim
-        rw [Nat.zero_add] at inv
-        rw [inv] at hlt
-        exact absurd hlt (Nat.lt_irrefl _)
-      | i+1, inv =>
-        if p as[j] then
-          some j
-        else
-          have : i + (j+1) = as.size := by
-            rw [← inv, Nat.add_comm j 1, Nat.add_assoc]
-          loop i (j+1) this
-    else
-      none
-  loop as.size 0 rfl
+  let rec loop (j : Nat) :=
+    if h : j < as.size then
+      if p as[j] then some j else loop (j + 1)
+    else none
+    termination_by as.size - j
+  loop 0
 
 def getIdx? [BEq α] (a : Array α) (v : α) : Option Nat :=
 a.findIdx? fun a => a == v
@@ -468,10 +487,18 @@ def elem [BEq α] (a : α) (as : Array α) : Bool :=
     else
       (true, r)
 
+/-- Convert a `Array α` into an `List α`. This is O(n) in the size of the array.  -/
+-- This function is exported to C, where it is called by `Array.data`
+-- (the projection) to implement this functionality.
 @[export lean_array_to_list]
 def toList (as : Array α) : List α :=
   as.foldr List.cons []
 
+/-- Prepends an `Array α` onto the front of a list.  Equivalent to `as.toList ++ l`. -/
+@[inline]
+def toListAppend (as : Array α) (l : List α) : List α :=
+  as.foldr List.cons l
+
 instance {α : Type u} [Repr α] : Repr (Array α) where
   reprPrec a _ :=
     let _ : Std.ToFormat α := ⟨repr⟩
@@ -501,6 +528,13 @@ def concatMapM [Monad m] (f : α → m (Array β)) (as : Array α) : m (Array β
 def concatMap (f : α → Array β) (as : Array α) : Array β :=
   as.foldl (init := empty) fun bs a => bs ++ f a
 
+/-- Joins array of array into a single array.
+
+`flatten #[#[a₁, a₂, ⋯], #[b₁, b₂, ⋯], ⋯]` = `#[a₁, a₂, ⋯, b₁, b₂, ⋯]`
+-/
+def flatten (as : Array (Array α)) : Array α :=
+  as.foldl (init := empty) fun r a => r ++ a
+
 end Array
 
 export Array (mkArray)
@@ -520,7 +554,7 @@ def isEqvAux (a b : Array α) (hsz : a.size = b.size) (p : α → α → Bool) (
      p a[i] b[i] && isEqvAux a b hsz p (i+1)
   else
     true
-termination_by _ => a.size - i
+termination_by a.size - i
 
 @[inline] def isEqv (a b : Array α) (p : α → α → Bool) : Bool :=
   if h : a.size = b.size then
@@ -624,7 +658,7 @@ def indexOfAux [BEq α] (a : Array α) (v : α) (i : Nat) : Option (Fin a.size)
     if a.get idx == v then some idx
     else indexOfAux a v (i+1)
   else none
-termination_by _ => a.size - i
+termination_by a.size - i
 
 def indexOf? [BEq α] (a : Array α) (v : α) : Option (Fin a.size) :=
   indexOfAux a v 0
@@ -656,7 +690,7 @@ where
       loop as (i+1) ⟨j-1, this⟩
     else
       as
-termination_by _ => j - i
+termination_by j - i
 
 def popWhile (p : α → Bool) (as : Array α) : Array α :=
   if h : as.size > 0 then
@@ -666,7 +700,7 @@ def popWhile (p : α → Bool) (as : Array α) : Array α :=
       as
   else
     as
-termination_by popWhile as => as.size
+termination_by as.size
 
 def takeWhile (p : α → Bool) (as : Array α) : Array α :=
   let rec go (i : Nat) (r : Array α) : Array α :=
@@ -678,36 +712,41 @@ def takeWhile (p : α → Bool) (as : Array α) : Array α :=
         r
     else
       r
+    termination_by as.size - i
   go 0 #[]
-termination_by go i r => as.size - i
 
-def eraseIdxAux (i : Nat) (a : Array α) : Array α :=
-  if h : i < a.size then
-    let idx  : Fin a.size := ⟨i, h⟩;
-    let idx1 : Fin a.size := ⟨i - 1, by exact Nat.lt_of_le_of_lt (Nat.pred_le i) h⟩;
-    let a' := a.swap idx idx1
-    eraseIdxAux (i+1) a'
+/-- Remove the element at a given index from an array without bounds checks, using a `Fin` index.
+
+  This function takes worst case O(n) time because
+  it has to backshift all elements at positions greater than `i`.-/
+def feraseIdx (a : Array α) (i : Fin a.size) : Array α :=
+  if h : i.val + 1 < a.size then
+    let a' := a.swap ⟨i.val + 1, h⟩ i
+    let i' : Fin a'.size := ⟨i.val + 1, by simp [a', h]⟩
+    have : a'.size - i' < a.size - i := by
+      simp [a', Nat.sub_succ_lt_self _ _ i.isLt]
+    a'.feraseIdx i'
   else
     a.pop
-termination_by _ => a.size - i
+termination_by a.size - i.val
 
-def feraseIdx (a : Array α) (i : Fin a.size) : Array α :=
-  eraseIdxAux (i.val + 1) a
+derive_functional_induction feraseIdx
 
+theorem size_feraseIdx (a : Array α) (i : Fin a.size) : (a.feraseIdx i).size = a.size - 1 := by
+  induction a, i using feraseIdx.induct with
+  | @case1 a i h a' _ _ ih =>
+    unfold feraseIdx
+    simp [h, a', ih]
+  | case2 a i h =>
+    unfold feraseIdx
+    simp [h]
+
+/-- Remove the element at a given index from an array, or do nothing if the index is out of bounds.
+
+  This function takes worst case O(n) time because
+  it has to backshift all elements at positions greater than `i`.-/
 def eraseIdx (a : Array α) (i : Nat) : Array α :=
-  if i < a.size then eraseIdxAux (i+1) a else a
-
-def eraseIdxSzAux (a : Array α) (i : Nat) (r : Array α) (heq : r.size = a.size) : { r : Array α // r.size = a.size - 1 } :=
-  if h : i < r.size then
-    let idx  : Fin r.size := ⟨i, h⟩;
-    let idx1 : Fin r.size := ⟨i - 1, by exact Nat.lt_of_le_of_lt (Nat.pred_le i) h⟩;
-    eraseIdxSzAux a (i+1) (r.swap idx idx1) ((size_swap r idx idx1).trans heq)
-  else
-    ⟨r.pop, (size_pop r).trans (heq ▸ rfl)⟩
-termination_by _ => r.size - i
-
-def eraseIdx' (a : Array α) (i : Fin a.size) : { r : Array α // r.size = a.size - 1 } :=
-  eraseIdxSzAux a (i.val + 1) a rfl
+  if h : i < a.size then a.feraseIdx ⟨i, h⟩ else a
 
 def erase [BEq α] (as : Array α) (a : α) : Array α :=
   match as.indexOf? a with
@@ -723,10 +762,10 @@ def erase [BEq α] (as : Array α) (a : α) : Array α :=
       loop as ⟨j', by rw [size_swap]; exact j'.2⟩
     else
       as
+    termination_by j.1
   let j := as.size
   let as := as.push a
   loop as ⟨j, size_push .. ▸ j.lt_succ_self⟩
-termination_by loop j => j.1
 
 /-- Insert element `a` at position `i`. Panics if `i` is not `i ≤ as.size`. -/
 def insertAt! (as : Array α) (i : Nat) (a : α) : Array α :=
@@ -763,7 +802,7 @@ where
     rfl
 
   go (i : Nat) (hi : i ≤ as.size) : toListLitAux as n hsz i hi (as.data.drop i) = as.data := by
-    cases i <;> simp [getLit_eq, List.get_drop_eq_drop, toListLitAux, List.drop, go]
+    induction i <;> simp [getLit_eq, List.get_drop_eq_drop, toListLitAux, List.drop, *]
 
 def isPrefixOfAux [BEq α] (as bs : Array α) (hle : as.size ≤ bs.size) (i : Nat) : Bool :=
   if h : i < as.size then
@@ -776,7 +815,7 @@ def isPrefixOfAux [BEq α] (as bs : Array α) (hle : as.size ≤ bs.size) (i : N
       false
   else
     true
-termination_by _ => as.size - i
+termination_by as.size - i
 
 /-- Return true iff `as` is a prefix of `bs`.
 That is, `bs = as ++ t` for some `t : List α`.-/
@@ -797,7 +836,7 @@ private def allDiffAux [BEq α] (as : Array α) (i : Nat) : Bool :=
     allDiffAuxAux as as[i] i h && allDiffAux as (i+1)
   else
     true
-termination_by _ => as.size - i
+termination_by as.size - i
 
 def allDiff [BEq α] (as : Array α) : Bool :=
   allDiffAux as 0
@@ -812,7 +851,7 @@ def allDiff [BEq α] (as : Array α) : Bool :=
       cs
   else
     cs
-termination_by _ => as.size - i
+termination_by as.size - i
 
 @[inline] def zipWith (as : Array α) (bs : Array β) (f : α → β → γ) : Array γ :=
   zipWithAux f as bs 0 #[]

src/Init/Data/Array/BasicAux.lean

@@ -47,7 +47,7 @@ where
       have hlt : i < as.size := Nat.lt_of_le_of_ne hle h
       let b ← f as[i]
       go (i+1) ⟨acc.val.push b, by simp [acc.property]⟩ hlt
-termination_by go i _ _ => as.size - i
+  termination_by as.size - i
 
 @[inline] private unsafe def mapMonoMImp [Monad m] (as : Array α) (f : α → m α) : m (Array α) :=
   go 0 as

src/Init/Data/Array/DecidableEq.lean

@@ -5,7 +5,7 @@ Authors: Leonardo de Moura
 -/
 prelude
 import Init.Data.Array.Basic
-import Init.Classical
+import Init.ByCases
 
 namespace Array
 
@@ -20,7 +20,7 @@ theorem eq_of_isEqvAux [DecidableEq α] (a b : Array α) (hsz : a.size = b.size)
   · have heq : i = a.size := Nat.le_antisymm hi (Nat.ge_of_not_lt h)
     subst heq
     exact absurd (Nat.lt_of_lt_of_le high low) (Nat.lt_irrefl j)
-termination_by _ => a.size - i
+termination_by a.size - i
 
 theorem eq_of_isEqv [DecidableEq α] (a b : Array α) : Array.isEqv a b (fun x y => x = y) → a = b := by
   simp [Array.isEqv]
@@ -36,7 +36,7 @@ theorem isEqvAux_self [DecidableEq α] (a : Array α) (i : Nat) : Array.isEqvAux
   split
   case inl h => simp [h, isEqvAux_self a (i+1)]
   case inr h => simp [h]
-termination_by _ => a.size - i
+termination_by a.size - i
 
 theorem isEqv_self [DecidableEq α] (a : Array α) : Array.isEqv a a (fun x y => x = y) = true := by
   simp [isEqv, isEqvAux_self]

src/Init/Data/Array/Lemmas.lean

@@ -0,0 +1,269 @@
+/-
+Copyright (c) 2022 Mario Carneiro. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Mario Carneiro
+-/
+prelude
+import Init.Data.Nat.MinMax
+import Init.Data.List.Lemmas
+import Init.Data.Fin.Basic
+import Init.Data.Array.Mem
+import Init.TacticsExtra
+
+/-!
+## Bootstrapping theorems about arrays
+
+This file contains some theorems about `Array` and `List` needed for `Std.List.Basic`.
+-/
+
+namespace Array
+
+attribute [simp] data_toArray uset
+
+@[simp] theorem mkEmpty_eq (α n) : @mkEmpty α n = #[] := rfl
+
+@[simp] theorem size_toArray (as : List α) : as.toArray.size = as.length := by simp [size]
+
+@[simp] theorem size_mk (as : List α) : (Array.mk as).size = as.length := by simp [size]
+
+theorem getElem_eq_data_get (a : Array α) (h : i < a.size) : a[i] = a.data.get ⟨i, h⟩ := by
+  by_cases i < a.size <;> (try simp [*]) <;> rfl
+
+theorem foldlM_eq_foldlM_data.aux [Monad m]
+    (f : β → α → m β) (arr : Array α) (i j) (H : arr.size ≤ i + j) (b) :
+    foldlM.loop f arr arr.size (Nat.le_refl _) i j b = (arr.data.drop j).foldlM f b := by
+  unfold foldlM.loop
+  split; split
+  · cases Nat.not_le_of_gt ‹_› (Nat.zero_add _ ▸ H)
+  · rename_i i; rw [Nat.succ_add] at H
+    simp [foldlM_eq_foldlM_data.aux f arr i (j+1) H]
+    rw (config := {occs := .pos [2]}) [← List.get_drop_eq_drop _ _ ‹_›]
+    rfl
+  · rw [List.drop_length_le (Nat.ge_of_not_lt ‹_›)]; rfl
+
+theorem foldlM_eq_foldlM_data [Monad m]
+    (f : β → α → m β) (init : β) (arr : Array α) :
+    arr.foldlM f init = arr.data.foldlM f init := by
+  simp [foldlM, foldlM_eq_foldlM_data.aux]
+
+theorem foldl_eq_foldl_data (f : β → α → β) (init : β) (arr : Array α) :
+    arr.foldl f init = arr.data.foldl f init :=
+  List.foldl_eq_foldlM .. ▸ foldlM_eq_foldlM_data ..
+
+theorem foldrM_eq_reverse_foldlM_data.aux [Monad m]
+    (f : α → β → m β) (arr : Array α) (init : β) (i h) :
+    (arr.data.take i).reverse.foldlM (fun x y => f y x) init = foldrM.fold f arr 0 i h init := by
+  unfold foldrM.fold
+  match i with
+  | 0 => simp [List.foldlM, List.take]
+  | i+1 => rw [← List.take_concat_get _ _ h]; simp [← (aux f arr · i)]; rfl
+
+theorem foldrM_eq_reverse_foldlM_data [Monad m] (f : α → β → m β) (init : β) (arr : Array α) :
+    arr.foldrM f init = arr.data.reverse.foldlM (fun x y => f y x) init := by
+  have : arr = #[] ∨ 0 < arr.size :=
+    match arr with | ⟨[]⟩ => .inl rfl | ⟨a::l⟩ => .inr (Nat.zero_lt_succ _)
+  match arr, this with | _, .inl rfl => rfl | arr, .inr h => ?_
+  simp [foldrM, h, ← foldrM_eq_reverse_foldlM_data.aux, List.take_length]
+
+theorem foldrM_eq_foldrM_data [Monad m]
+    (f : α → β → m β) (init : β) (arr : Array α) :
+    arr.foldrM f init = arr.data.foldrM f init := by
+  rw [foldrM_eq_reverse_foldlM_data, List.foldlM_reverse]
+
+theorem foldr_eq_foldr_data (f : α → β → β) (init : β) (arr : Array α) :
+    arr.foldr f init = arr.data.foldr f init :=
+  List.foldr_eq_foldrM .. ▸ foldrM_eq_foldrM_data ..
+
+@[simp] theorem push_data (arr : Array α) (a : α) : (arr.push a).data = arr.data ++ [a] := by
+  simp [push, List.concat_eq_append]
+
+theorem foldrM_push [Monad m] (f : α → β → m β) (init : β) (arr : Array α) (a : α) :
+    (arr.push a).foldrM f init = f a init >>= arr.foldrM f := by
+  simp [foldrM_eq_reverse_foldlM_data, -size_push]
+
+@[simp] theorem foldrM_push' [Monad m] (f : α → β → m β) (init : β) (arr : Array α) (a : α) :
+    (arr.push a).foldrM f init (start := arr.size + 1) = f a init >>= arr.foldrM f := by
+  simp [← foldrM_push]
+
+theorem foldr_push (f : α → β → β) (init : β) (arr : Array α) (a : α) :
+    (arr.push a).foldr f init = arr.foldr f (f a init) := foldrM_push ..
+
+@[simp] theorem foldr_push' (f : α → β → β) (init : β) (arr : Array α) (a : α) :
+    (arr.push a).foldr f init (start := arr.size + 1) = arr.foldr f (f a init) := foldrM_push' ..
+
+@[simp] theorem toListAppend_eq (arr : Array α) (l) : arr.toListAppend l = arr.data ++ l := by
+  simp [toListAppend, foldr_eq_foldr_data]
+
+@[simp] theorem toList_eq (arr : Array α) : arr.toList = arr.data := by
+  simp [toList, foldr_eq_foldr_data]
+
+/-- A more efficient version of `arr.toList.reverse`. -/
+@[inline] def toListRev (arr : Array α) : List α := arr.foldl (fun l t => t :: l) []
+
+@[simp] theorem toListRev_eq (arr : Array α) : arr.toListRev = arr.data.reverse := by
+  rw [toListRev, foldl_eq_foldl_data, ← List.foldr_reverse, List.foldr_self]
+
+theorem get_push_lt (a : Array α) (x : α) (i : Nat) (h : i < a.size) :
+    have : i < (a.push x).size := by simp [*, Nat.lt_succ_of_le, Nat.le_of_lt]
+    (a.push x)[i] = a[i] := by
+  simp only [push, getElem_eq_data_get, List.concat_eq_append, List.get_append_left, h]
+
+@[simp] theorem get_push_eq (a : Array α) (x : α) : (a.push x)[a.size] = x := by
+  simp only [push, getElem_eq_data_get, List.concat_eq_append]
+  rw [List.get_append_right] <;> simp [getElem_eq_data_get, Nat.zero_lt_one]
+
+theorem get_push (a : Array α) (x : α) (i : Nat) (h : i < (a.push x).size) :
+    (a.push x)[i] = if h : i < a.size then a[i] else x := by
+  by_cases h' : i < a.size
+  · simp [get_push_lt, h']
+  · simp at h
+    simp [get_push_lt, Nat.le_antisymm (Nat.le_of_lt_succ h) (Nat.ge_of_not_lt h')]
+
+theorem mapM_eq_foldlM [Monad m] [LawfulMonad m] (f : α → m β) (arr : Array α) :
+    arr.mapM f = arr.foldlM (fun bs a => bs.push <$> f a) #[] := by
+  rw [mapM, aux, foldlM_eq_foldlM_data]; rfl
+where
+  aux (i r) :
+      mapM.map f arr i r = (arr.data.drop i).foldlM (fun bs a => bs.push <$> f a) r := by
+    unfold mapM.map; split
+    · rw [← List.get_drop_eq_drop _ i ‹_›]
+      simp [aux (i+1), map_eq_pure_bind]; rfl
+    · rw [List.drop_length_le (Nat.ge_of_not_lt ‹_›)]; rfl
+  termination_by arr.size - i
+
+@[simp] theorem map_data (f : α → β) (arr : Array α) : (arr.map f).data = arr.data.map f := by
+  rw [map, mapM_eq_foldlM]
+  apply congrArg data (foldl_eq_foldl_data (fun bs a => push bs (f a)) #[] arr) |>.trans
+  have H (l arr) : List.foldl (fun bs a => push bs (f a)) arr l = ⟨arr.data ++ l.map f⟩ := by
+    induction l generalizing arr <;> simp [*]
+  simp [H]
+
+@[simp] theorem size_map (f : α → β) (arr : Array α) : (arr.map f).size = arr.size := by
+  simp [size]
+
+@[simp] theorem pop_data (arr : Array α) : arr.pop.data = arr.data.dropLast := rfl
+
+@[simp] theorem append_eq_append (arr arr' : Array α) : arr.append arr' = arr ++ arr' := rfl
+
+@[simp] theorem append_data (arr arr' : Array α) :
+    (arr ++ arr').data = arr.data ++ arr'.data := by
+  rw [← append_eq_append]; unfold Array.append
+  rw [foldl_eq_foldl_data]
+  induction arr'.data generalizing arr <;> simp [*]
+
+@[simp] theorem appendList_eq_append
+    (arr : Array α) (l : List α) : arr.appendList l = arr ++ l := rfl
+
+@[simp] theorem appendList_data (arr : Array α) (l : List α) :
+    (arr ++ l).data = arr.data ++ l := by
+  rw [← appendList_eq_append]; unfold Array.appendList
+  induction l generalizing arr <;> simp [*]
+
+@[simp] theorem appendList_nil (arr : Array α) : arr ++ ([] : List α) = arr := Array.ext' (by simp)
+
+@[simp] theorem appendList_cons (arr : Array α) (a : α) (l : List α) :
+    arr ++ (a :: l) = arr.push a ++ l := Array.ext' (by simp)
+
+theorem foldl_data_eq_bind (l : List α) (acc : Array β)
+    (F : Array β → α → Array β) (G : α → List β)
+    (H : ∀ acc a, (F acc a).data = acc.data ++ G a) :
+    (l.foldl F acc).data = acc.data ++ l.bind G := by
+  induction l generalizing acc <;> simp [*, List.bind]
+
+theorem foldl_data_eq_map (l : List α) (acc : Array β) (G : α → β) :
+    (l.foldl (fun acc a => acc.push (G a)) acc).data = acc.data ++ l.map G := by
+  induction l generalizing acc <;> simp [*]
+
+theorem size_uset (a : Array α) (v i h) : (uset a i v h).size = a.size := by simp
+
+theorem anyM_eq_anyM_loop [Monad m] (p : α → m Bool) (as : Array α) (start stop) :
+    anyM p as start stop = anyM.loop p as (min stop as.size) (Nat.min_le_right ..) start := by
+  simp only [anyM, Nat.min_def]; split <;> rfl
+
+theorem anyM_stop_le_start [Monad m] (p : α → m Bool) (as : Array α) (start stop)
+    (h : min stop as.size ≤ start) : anyM p as start stop = pure false := by
+  rw [anyM_eq_anyM_loop, anyM.loop, dif_neg (Nat.not_lt.2 h)]
+
+theorem mem_def (a : α) (as : Array α) : a ∈ as ↔ a ∈ as.data :=
+  ⟨fun | .mk h => h, Array.Mem.mk⟩
+
+/-- # get -/
+@[simp] theorem get_eq_getElem (a : Array α) (i : Fin _) : a.get i = a[i.1] := rfl
+
+theorem getElem?_lt
+    (a : Array α) {i : Nat} (h : i < a.size) : a[i]? = some (a[i]) := dif_pos h
+
+theorem getElem?_ge
+    (a : Array α) {i : Nat} (h : i ≥ a.size) : a[i]? = none := dif_neg (Nat.not_lt_of_le h)
+
+@[simp] theorem get?_eq_getElem? (a : Array α) (i : Nat) : a.get? i = a[i]? := rfl
+
+theorem getElem?_len_le (a : Array α) {i : Nat} (h : a.size ≤ i) : a[i]? = none := by
+  simp [getElem?_ge, h]
+
+theorem getD_get? (a : Array α) (i : Nat) (d : α) :
+  Option.getD a[i]? d = if p : i < a.size then a[i]'p else d := by
+  if h : i < a.size then
+    simp [setD, h, getElem?]
+  else
+    have p : i ≥ a.size := Nat.le_of_not_gt h
+    simp [setD, getElem?_len_le _ p, h]
+
+@[simp] theorem getD_eq_get? (a : Array α) (n d) : a.getD n d = (a[n]?).getD d := by
+  simp only [getD, get_eq_getElem, get?_eq_getElem?]; split <;> simp [getD_get?, *]
+
+theorem get!_eq_getD [Inhabited α] (a : Array α) : a.get! n = a.getD n default := rfl
+
+@[simp] theorem get!_eq_getElem? [Inhabited α] (a : Array α) (i : Nat) : a.get! i = (a.get? i).getD default := by
+  by_cases p : i < a.size <;> simp [getD_get?, get!_eq_getD, p]
+
+/-- # set -/
+
+@[simp] theorem getElem_set_eq (a : Array α) (i : Fin a.size) (v : α) {j : Nat}
+      (eq : i.val = j) (p : j < (a.set i v).size) :
+    (a.set i v)[j]'p = v := by
+  simp [set, getElem_eq_data_get, ←eq]
+
+@[simp] theorem getElem_set_ne (a : Array α) (i : Fin a.size) (v : α) {j : Nat} (pj : j < (a.set i v).size)
+    (h : i.val ≠ j) : (a.set i v)[j]'pj = a[j]'(size_set a i v ▸ pj) := by
+  simp only [set, getElem_eq_data_get, List.get_set_ne _ h]
+
+theorem getElem_set (a : Array α) (i : Fin a.size) (v : α) (j : Nat)
+    (h : j < (a.set i v).size) :
+    (a.set i v)[j]'h = if i = j then v else a[j]'(size_set a i v ▸ h) := by
+  by_cases p : i.1 = j <;> simp [p]
+
+@[simp] theorem getElem?_set_eq (a : Array α) (i : Fin a.size) (v : α) :
+    (a.set i v)[i.1]? = v := by simp [getElem?_lt, i.2]
+
+@[simp] theorem getElem?_set_ne (a : Array α) (i : Fin a.size) {j : Nat} (v : α)
+    (ne : i.val ≠ j) : (a.set i v)[j]? = a[j]? := by
+  by_cases h : j < a.size <;> simp [getElem?_lt, getElem?_ge, Nat.ge_of_not_lt, ne, h]
+
+/- # setD -/
+
+@[simp] theorem set!_is_setD : @set! = @setD := rfl
+
+@[simp] theorem size_setD (a : Array α) (index : Nat) (val : α) :
+  (Array.setD a index val).size = a.size := by
+  if h : index < a.size  then
+    simp [setD, h]
+  else
+    simp [setD, h]
+
+@[simp] theorem getElem_setD_eq (a : Array α) {i : Nat} (v : α) (h : _) :
+  (setD a i v)[i]'h = v := by
+  simp at h
+  simp only [setD, h, dite_true, getElem_set, ite_true]
+
+@[simp]
+theorem getElem?_setD_eq (a : Array α) {i : Nat} (p : i < a.size) (v : α) : (a.setD i v)[i]? = some v := by
+  simp [getElem?_lt, p]
+
+/-- Simplifies a normal form from `get!` -/
+@[simp] theorem getD_get?_setD (a : Array α) (i : Nat) (v d : α) :
+  Option.getD (setD a i v)[i]? d = if i < a.size then v else d := by
+  by_cases h : i < a.size <;>
+    simp [setD, Nat.not_lt_of_le, h,  getD_get?]
+
+end Array

src/Init/Data/Array/Mem.lean

@@ -1,51 +1,31 @@
 /-
 Copyright (c) 2022 Microsoft Corporation. All rights reserved.
 Released under Apache 2.0 license as described in the file LICENSE.
-Authors: Leonardo de Moura
+Authors: Leonardo de Moura, Joachim Breitner
 -/
 prelude
 import Init.Data.Array.Basic
 import Init.Data.Nat.Linear
 import Init.Data.List.BasicAux
 
-theorem List.sizeOf_get_lt [SizeOf α] (as : List α) (i : Fin as.length) : sizeOf (as.get i) < sizeOf as := by
-  match as, i with
-  | [],    i      => apply Fin.elim0 i
-  | a::as, ⟨0, _⟩ => simp_arith [get]
-  | a::as, ⟨i+1, h⟩ =>
-    simp [get]
-    have h : i < as.length := Nat.lt_of_succ_lt_succ h
-    have ih := sizeOf_get_lt as ⟨i, h⟩
-    exact Nat.lt_of_lt_of_le ih (Nat.le_add_left ..)
-
 namespace Array
 
-instance [DecidableEq α] : Membership α (Array α) where
-  mem a as := as.contains a
+/-- `a ∈ as` is a predicate which asserts that `a` is in the array `as`. -/
+-- NB: This is defined as a structure rather than a plain def so that a lemma
+-- like `sizeOf_lt_of_mem` will not apply with no actual arrays around.
+structure Mem (a : α) (as : Array α) : Prop where
+  val : a ∈ as.data
 
-theorem sizeOf_get_lt [SizeOf α] (as : Array α) (i : Fin as.size) : sizeOf (as.get i) < sizeOf as := by
-  cases as; rename_i as
-  simp [get]
-  have ih := List.sizeOf_get_lt as i
-  exact Nat.lt_trans ih (by simp_arith)
+instance : Membership α (Array α) where
+  mem a as := Mem a as
 
-theorem sizeOf_lt_of_mem [DecidableEq α] [SizeOf α] {as : Array α} (h : a ∈ as) : sizeOf a < sizeOf as := by
-  simp [Membership.mem, contains, any, Id.run, BEq.beq, anyM] at h
-  let rec aux (j : Nat) (h : anyM.loop (m := Id) (fun b => decide (a = b)) as as.size (Nat.le_refl ..) j = true) : sizeOf a < sizeOf as := by
-    unfold anyM.loop at h
-    split at h
-    · simp [Bind.bind, pure] at h; split at h
-      next he => subst a; apply sizeOf_get_lt
-      next => have ih := aux (j+1) h; assumption
-    · contradiction
-  apply aux 0 h
-termination_by aux j _ => as.size - j
+theorem sizeOf_lt_of_mem [SizeOf α] {as : Array α} (h : a ∈ as) : sizeOf a < sizeOf as := by
+  cases as with | _ as =>
+  exact Nat.lt_trans (List.sizeOf_lt_of_mem h.val) (by simp_arith)
 
 @[simp] theorem sizeOf_get [SizeOf α] (as : Array α) (i : Fin as.size) : sizeOf (as.get i) < sizeOf as := by
-  cases as
-  simp [get]
-  apply Nat.lt_trans (List.sizeOf_get ..)
-  simp_arith
+  cases as with | _ as =>
+  exact Nat.lt_trans (List.sizeOf_get ..) (by simp_arith)
 
 /-- This tactic, added to the `decreasing_trivial` toolbox, proves that
 `sizeOf arr[i] < sizeOf arr`, which is useful for well founded recursions
@@ -57,4 +37,17 @@ macro "array_get_dec" : tactic =>
 
 macro_rules | `(tactic| decreasing_trivial) => `(tactic| array_get_dec)
 
+/-- This tactic, added to the `decreasing_trivial` toolbox, proves that `sizeOf a < sizeOf arr`
+provided that `a ∈ arr` which is useful for well founded recursions over a nested inductive like
+`inductive T | mk : Array T → T`. -/
+-- NB: This is analogue to tactic `sizeOf_list_dec`
+macro "array_mem_dec" : tactic =>
+  `(tactic| first
+    | apply Array.sizeOf_lt_of_mem; assumption; done
+    | apply Nat.lt_trans (Array.sizeOf_lt_of_mem ?h)
+      case' h => assumption
+      simp_arith)
+
+macro_rules | `(tactic| decreasing_trivial) => `(tactic| array_mem_dec)
+
 end Array

src/Init/Data/Array/QSort.lean

@@ -10,7 +10,7 @@ namespace Array
 -- TODO: remove the [Inhabited α] parameters as soon as we have the tactic framework for automating proof generation and using Array.fget
 
 def qpartition (as : Array α) (lt : α → α → Bool) (lo hi : Nat) : Nat × Array α :=
-  if h : as.size = 0 then (0, as) else have : Inhabited α := ⟨as[0]'(by revert h; cases as.size <;> simp [Nat.zero_lt_succ])⟩ -- TODO: remove
+  if h : as.size = 0 then (0, as) else have : Inhabited α := ⟨as[0]'(by revert h; cases as.size <;> simp)⟩ -- TODO: remove
   let mid := (lo + hi) / 2
   let as  := if lt (as.get! mid) (as.get! lo) then as.swap! lo mid else as
   let as  := if lt (as.get! hi)  (as.get! lo) then as.swap! lo hi  else as
@@ -26,8 +26,8 @@ def qpartition (as : Array α) (lt : α → α → Bool) (lo hi : Nat) : Nat ×
     else
       let as := as.swap! i hi
       (i, as)
+    termination_by hi - j
   loop as lo lo
-termination_by _ => hi - j
 
 @[inline] partial def qsort (as : Array α) (lt : α → α → Bool) (low := 0) (high := as.size - 1) : Array α :=
   let rec @[specialize] sort (as : Array α) (low high : Nat) :=

src/Init/Data/Array/Subarray.lean

@@ -143,6 +143,7 @@ def toSubarray (as : Array α) (start : Nat := 0) (stop : Nat := as.size) : Suba
      else
        { as := as, start := as.size, stop := as.size, h₁ := Nat.le_refl _, h₂ := Nat.le_refl _ }
 
+@[coe]
 def ofSubarray (s : Subarray α) : Array α := Id.run do
   let mut as := mkEmpty (s.stop - s.start)
   for a in s do

src/Init/Data/BitVec.lean

@@ -0,0 +1,10 @@
+/-
+Copyright (c) 2024 Lean FRO, LLC. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Scott Morrison
+-/
+prelude
+import Init.Data.BitVec.Basic
+import Init.Data.BitVec.Bitblast
+import Init.Data.BitVec.Folds
+import Init.Data.BitVec.Lemmas

src/Init/Data/BitVec/Basic.lean

@@ -0,0 +1,631 @@
+/-
+Copyright (c) 2024 Lean FRO, LLC. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Joe Hendrix, Wojciech Nawrocki, Leonardo de Moura, Mario Carneiro, Alex Keizer
+-/
+prelude
+import Init.Data.Fin.Basic
+import Init.Data.Nat.Bitwise.Lemmas
+import Init.Data.Nat.Power2
+import Init.Data.Int.Bitwise
+
+/-!
+We define bitvectors. We choose the `Fin` representation over others for its relative efficiency
+(Lean has special support for `Nat`), alignment with `UIntXY` types which are also represented
+with `Fin`, and the fact that bitwise operations on `Fin` are already defined. Some other possible
+representations are `List Bool`, `{ l : List Bool // l.length = w }`, `Fin w → Bool`.
+
+We define many of the bitvector operations from the
+[`QF_BV` logic](https://smtlib.cs.uiowa.edu/logics-all.shtml#QF_BV).
+of SMT-LIBv2.
+-/
+
+/--
+A bitvector of the specified width.
+
+This is represented as the underlying `Nat` number in both the runtime
+and the kernel, inheriting all the special support for `Nat`.
+-/
+structure BitVec (w : Nat) where
+  /-- Construct a `BitVec w` from a number less than `2^w`.
+  O(1), because we use `Fin` as the internal representation of a bitvector. -/
+  ofFin ::
+  /-- Interpret a bitvector as a number less than `2^w`.
+  O(1), because we use `Fin` as the internal representation of a bitvector. -/
+  toFin : Fin (2^w)
+
+@[deprecated] abbrev Std.BitVec := _root_.BitVec
+
+-- We manually derive the `DecidableEq` instances for `BitVec` because
+-- we want to have builtin support for bit-vector literals, and we
+-- need a name for this function to implement `canUnfoldAtMatcher` at `WHNF.lean`.
+def BitVec.decEq (a b : BitVec n) : Decidable (a = b) :=
+  match a, b with
+  | ⟨n⟩, ⟨m⟩ =>
+    if h : n = m then
+      isTrue (h ▸ rfl)
+    else
+      isFalse (fun h' => BitVec.noConfusion h' (fun h' => absurd h' h))
+
+instance : DecidableEq (BitVec n) := BitVec.decEq
+
+namespace BitVec
+
+section Nat
+
+/-- The `BitVec` with value `i`, given a proof that `i < 2^n`. -/
+@[match_pattern]
+protected def ofNatLt {n : Nat} (i : Nat) (p : i < 2^n) : BitVec n where
+  toFin := ⟨i, p⟩
+
+/-- The `BitVec` with value `i mod 2^n`. -/
+@[match_pattern]
+protected def ofNat (n : Nat) (i : Nat) : BitVec n where
+  toFin := Fin.ofNat' i (Nat.two_pow_pos n)
+
+instance instOfNat : OfNat (BitVec n) i where ofNat := .ofNat n i
+instance natCastInst : NatCast (BitVec w) := ⟨BitVec.ofNat w⟩
+
+/-- Given a bitvector `a`, return the underlying `Nat`. This is O(1) because `BitVec` is a
+(zero-cost) wrapper around a `Nat`. -/
+protected def toNat (a : BitVec n) : Nat := a.toFin.val
+
+/-- Return the bound in terms of toNat. -/
+theorem isLt (x : BitVec w) : x.toNat < 2^w := x.toFin.isLt
+
+@[deprecated isLt]
+theorem toNat_lt (x : BitVec n) : x.toNat < 2^n := x.isLt
+
+/-- Theorem for normalizing the bit vector literal representation. -/
+-- TODO: This needs more usage data to assess which direction the simp should go.
+@[simp, bv_toNat] theorem ofNat_eq_ofNat : @OfNat.ofNat (BitVec n) i _ = .ofNat n i := rfl
+
+-- Note. Mathlib would like this to go the other direction.
+@[simp] theorem natCast_eq_ofNat (w x : Nat) : @Nat.cast (BitVec w) _ x = .ofNat w x := rfl
+
+end Nat
+
+section subsingleton
+
+/-- All empty bitvectors are equal -/
+instance : Subsingleton (BitVec 0) where
+  allEq := by intro ⟨0, _⟩ ⟨0, _⟩; rfl
+
+/-- The empty bitvector -/
+abbrev nil : BitVec 0 := 0
+
+/-- Every bitvector of length 0 is equal to `nil`, i.e., there is only one empty bitvector -/
+theorem eq_nil (x : BitVec 0) : x = nil := Subsingleton.allEq ..
+
+end subsingleton
+
+section zero_allOnes
+
+/-- Return a bitvector `0` of size `n`. This is the bitvector with all zero bits. -/
+protected def zero (n : Nat) : BitVec n := .ofNatLt 0 (Nat.two_pow_pos n)
+instance : Inhabited (BitVec n) where default := .zero n
+
+/-- Bit vector of size `n` where all bits are `1`s -/
+def allOnes (n : Nat) : BitVec n :=
+  .ofNatLt (2^n - 1) (Nat.le_of_eq (Nat.sub_add_cancel (Nat.two_pow_pos n)))
+
+end zero_allOnes
+
+section getXsb
+
+/-- Return the `i`-th least significant bit or `false` if `i ≥ w`. -/
+@[inline] def getLsb (x : BitVec w) (i : Nat) : Bool := x.toNat.testBit i
+
+/-- Return the `i`-th most significant bit or `false` if `i ≥ w`. -/
+@[inline] def getMsb (x : BitVec w) (i : Nat) : Bool := i < w && getLsb x (w-1-i)
+
+/-- Return most-significant bit in bitvector. -/
+@[inline] protected def msb (a : BitVec n) : Bool := getMsb a 0
+
+end getXsb
+
+section Int
+
+/-- Interpret the bitvector as an integer stored in two's complement form. -/
+protected def toInt (a : BitVec n) : Int :=
+  if 2 * a.toNat < 2^n then
+    a.toNat
+  else
+    (a.toNat : Int) - (2^n : Nat)
+
+/-- The `BitVec` with value `(2^n + (i mod 2^n)) mod 2^n`.  -/
+protected def ofInt (n : Nat) (i : Int) : BitVec n := .ofNatLt (i % (Int.ofNat (2^n))).toNat (by
+  apply (Int.toNat_lt _).mpr
+  · apply Int.emod_lt_of_pos
+    exact Int.ofNat_pos.mpr (Nat.two_pow_pos _)
+  · apply Int.emod_nonneg
+    intro eq
+    apply Nat.ne_of_gt (Nat.two_pow_pos n)
+    exact Int.ofNat_inj.mp eq)
+
+instance : IntCast (BitVec w) := ⟨BitVec.ofInt w⟩
+
+end Int
+
+section Syntax
+
+/-- Notation for bit vector literals. `i#n` is a shorthand for `BitVec.ofNat n i`. -/
+scoped syntax:max term:max noWs "#" noWs term:max : term
+macro_rules | `($i#$n) => `(BitVec.ofNat $n $i)
+
+/-- Unexpander for bit vector literals. -/
+@[app_unexpander BitVec.ofNat] def unexpandBitVecOfNat : Lean.PrettyPrinter.Unexpander
+  | `($(_) $n $i) => `($i#$n)
+  | _ => throw ()
+
+/-- Notation for bit vector literals without truncation. `i#'lt` is a shorthand for `BitVec.ofNatLt i lt`. -/
+scoped syntax:max term:max noWs "#'" noWs term:max : term
+macro_rules | `($i#'$p) => `(BitVec.ofNatLt $i $p)
+
+/-- Unexpander for bit vector literals without truncation. -/
+@[app_unexpander BitVec.ofNatLt] def unexpandBitVecOfNatLt : Lean.PrettyPrinter.Unexpander
+  | `($(_) $i $p) => `($i#'$p)
+  | _ => throw ()
+
+end Syntax
+
+section repr_toString
+
+/-- Convert bitvector into a fixed-width hex number. -/
+protected def toHex {n : Nat} (x : BitVec n) : String :=
+  let s := (Nat.toDigits 16 x.toNat).asString
+  let t := (List.replicate ((n+3) / 4 - s.length) '0').asString
+  t ++ s
+
+instance : Repr (BitVec n) where reprPrec a _ := "0x" ++ (a.toHex : Std.Format) ++ "#" ++ repr n
+instance : ToString (BitVec n) where toString a := toString (repr a)
+
+end repr_toString
+
+section arithmetic
+
+/--
+Addition for bit vectors. This can be interpreted as either signed or unsigned addition
+modulo `2^n`.
+
+SMT-Lib name: `bvadd`.
+-/
+protected def add (x y : BitVec n) : BitVec n := .ofNat n (x.toNat + y.toNat)
+instance : Add (BitVec n) := ⟨BitVec.add⟩
+
+/--
+Subtraction for bit vectors. This can be interpreted as either signed or unsigned subtraction
+modulo `2^n`.
+-/
+protected def sub (x y : BitVec n) : BitVec n := .ofNat n (x.toNat + (2^n - y.toNat))
+instance : Sub (BitVec n) := ⟨BitVec.sub⟩
+
+/--
+Negation for bit vectors. This can be interpreted as either signed or unsigned negation
+modulo `2^n`.
+
+SMT-Lib name: `bvneg`.
+-/
+protected def neg (x : BitVec n) : BitVec n := .ofNat n (2^n - x.toNat)
+instance : Neg (BitVec n) := ⟨.neg⟩
+
+/--
+Return the absolute value of a signed bitvector.
+-/
+protected def abs (s : BitVec n) : BitVec n := if s.msb then .neg s else s
+
+/--
+Multiplication for bit vectors. This can be interpreted as either signed or unsigned negation
+modulo `2^n`.
+
+SMT-Lib name: `bvmul`.
+-/
+protected def mul (x y : BitVec n) : BitVec n := BitVec.ofNat n (x.toNat * y.toNat)
+instance : Mul (BitVec n) := ⟨.mul⟩
+
+/--
+Unsigned division for bit vectors using the Lean convention where division by zero returns zero.
+-/
+def udiv (x y : BitVec n) : BitVec n :=
+  (x.toNat / y.toNat)#'(Nat.lt_of_le_of_lt (Nat.div_le_self _ _) x.isLt)
+instance : Div (BitVec n) := ⟨.udiv⟩
+
+/--
+Unsigned modulo for bit vectors.
+
+SMT-Lib name: `bvurem`.
+-/
+def umod (x y : BitVec n) : BitVec n :=
+  (x.toNat % y.toNat)#'(Nat.lt_of_le_of_lt (Nat.mod_le _ _) x.isLt)
+instance : Mod (BitVec n) := ⟨.umod⟩
+
+/--
+Unsigned division for bit vectors using the
+[SMT-Lib convention](http://smtlib.cs.uiowa.edu/theories-FixedSizeBitVectors.shtml)
+where division by zero returns the `allOnes` bitvector.
+
+SMT-Lib name: `bvudiv`.
+-/
+def smtUDiv (x y : BitVec n) : BitVec n := if y = 0 then allOnes n else udiv x y
+
+/--
+Signed t-division for bit vectors using the Lean convention where division
+by zero returns zero.
+
+```lean
+sdiv 7#4 2 = 3#4
+sdiv (-9#4) 2 = -4#4
+sdiv 5#4 -2 = -2#4
+sdiv (-7#4) (-2) = 3#4
+```
+-/
+def sdiv (s t : BitVec n) : BitVec n :=
+  match s.msb, t.msb with
+  | false, false => udiv s t
+  | false, true  => .neg (udiv s (.neg t))
+  | true,  false => .neg (udiv (.neg s) t)
+  | true,  true  => udiv (.neg s) (.neg t)
+
+/--
+Signed division for bit vectors using SMTLIB rules for division by zero.
+
+Specifically, `smtSDiv x 0 = if x >= 0 then -1 else 1`
+
+SMT-Lib name: `bvsdiv`.
+-/
+def smtSDiv (s t : BitVec n) : BitVec n :=
+  match s.msb, t.msb with
+  | false, false => smtUDiv s t
+  | false, true  => .neg (smtUDiv s (.neg t))
+  | true,  false => .neg (smtUDiv (.neg s) t)
+  | true,  true  => smtUDiv (.neg s) (.neg t)
+
+/--
+Remainder for signed division rounding to zero.
+
+SMT_Lib name: `bvsrem`.
+-/
+def srem (s t : BitVec n) : BitVec n :=
+  match s.msb, t.msb with
+  | false, false => umod s t
+  | false, true  => umod s (.neg t)
+  | true,  false => .neg (umod (.neg s) t)
+  | true,  true  => .neg (umod (.neg s) (.neg t))
+
+/--
+Remainder for signed division rounded to negative infinity.
+
+SMT_Lib name: `bvsmod`.
+-/
+def smod (s t : BitVec m) : BitVec m :=
+  match s.msb, t.msb with
+  | false, false => umod s t
+  | false, true =>
+    let u := umod s (.neg t)
+    (if u = .zero m then u else .add u t)
+  | true, false =>
+    let u := umod (.neg s) t
+    (if u = .zero m then u else .sub t u)
+  | true, true => .neg (umod (.neg s) (.neg t))
+
+end arithmetic
+
+
+section bool
+
+/-- Turn a `Bool` into a bitvector of length `1` -/
+def ofBool (b : Bool) : BitVec 1 := cond b 1 0
+
+@[simp] theorem ofBool_false : ofBool false = 0 := by trivial
+@[simp] theorem ofBool_true  : ofBool true  = 1 := by trivial
+
+/-- Fills a bitvector with `w` copies of the bit `b`. -/
+def fill (w : Nat) (b : Bool) : BitVec w := bif b then -1 else 0
+
+end bool
+
+section relations
+
+/--
+Unsigned less-than for bit vectors.
+
+SMT-Lib name: `bvult`.
+-/
+protected def ult (x y : BitVec n) : Bool := x.toNat < y.toNat
+
+instance : LT (BitVec n) where lt := (·.toNat < ·.toNat)
+instance (x y : BitVec n) : Decidable (x < y) :=
+  inferInstanceAs (Decidable (x.toNat < y.toNat))
+
+/--
+Unsigned less-than-or-equal-to for bit vectors.
+
+SMT-Lib name: `bvule`.
+-/
+protected def ule (x y : BitVec n) : Bool := x.toNat ≤ y.toNat
+
+instance : LE (BitVec n) where le := (·.toNat ≤ ·.toNat)
+instance (x y : BitVec n) : Decidable (x ≤ y) :=
+  inferInstanceAs (Decidable (x.toNat ≤ y.toNat))
+
+/--
+Signed less-than for bit vectors.
+
+```lean
+BitVec.slt 6#4 7 = true
+BitVec.slt 7#4 8 = false
+```
+SMT-Lib name: `bvslt`.
+-/
+protected def slt (x y : BitVec n) : Bool := x.toInt < y.toInt
+
+/--
+Signed less-than-or-equal-to for bit vectors.
+
+SMT-Lib name: `bvsle`.
+-/
+protected def sle (x y : BitVec n) : Bool := x.toInt ≤ y.toInt
+
+end relations
+
+section cast
+
+/-- `cast eq i` embeds `i` into an equal `BitVec` type. -/
+@[inline] def cast (eq : n = m) (i : BitVec n) : BitVec m := .ofNatLt i.toNat (eq ▸ i.isLt)
+
+@[simp] theorem cast_ofNat {n m : Nat} (h : n = m) (x : Nat) :
+    cast h (BitVec.ofNat n x) = BitVec.ofNat m x := by
+  subst h; rfl
+
+@[simp] theorem cast_cast {n m k : Nat} (h₁ : n = m) (h₂ : m = k) (x : BitVec n) :
+    cast h₂ (cast h₁ x) = cast (h₁ ▸ h₂) x :=
+  rfl
+
+@[simp] theorem cast_eq {n : Nat} (h : n = n) (x : BitVec n) : cast h x = x := rfl
+
+/--
+Extraction of bits `start` to `start + len - 1` from a bit vector of size `n` to yield a
+new bitvector of size `len`. If `start + len > n`, then the vector will be zero-padded in the
+high bits.
+-/
+def extractLsb' (start len : Nat) (a : BitVec n) : BitVec len := .ofNat _ (a.toNat >>> start)
+
+/--
+Extraction of bits `hi` (inclusive) down to `lo` (inclusive) from a bit vector of size `n` to
+yield a new bitvector of size `hi - lo + 1`.
+
+SMT-Lib name: `extract`.
+-/
+def extractLsb (hi lo : Nat) (a : BitVec n) : BitVec (hi - lo + 1) := extractLsb' lo _ a
+
+/--
+A version of `zeroExtend` that requires a proof, but is a noop.
+-/
+def zeroExtend' {n w : Nat} (le : n ≤ w) (x : BitVec n)  : BitVec w :=
+  x.toNat#'(by
+    apply Nat.lt_of_lt_of_le x.isLt
+    exact Nat.pow_le_pow_of_le_right (by trivial) le)
+
+/--
+`shiftLeftZeroExtend x n` returns `zeroExtend (w+n) x <<< n` without
+needing to compute `x % 2^(2+n)`.
+-/
+def shiftLeftZeroExtend (msbs : BitVec w) (m : Nat) : BitVec (w+m) :=
+  let shiftLeftLt {x : Nat} (p : x < 2^w) (m : Nat) : x <<< m < 2^(w+m) := by
+        simp [Nat.shiftLeft_eq, Nat.pow_add]
+        apply Nat.mul_lt_mul_of_pos_right p
+        exact (Nat.two_pow_pos m)
+  (msbs.toNat <<< m)#'(shiftLeftLt msbs.isLt m)
+
+/--
+Zero extend vector `x` of length `w` by adding zeros in the high bits until it has length `v`.
+If `v < w` then it truncates the high bits instead.
+
+SMT-Lib name: `zero_extend`.
+-/
+def zeroExtend (v : Nat) (x : BitVec w) : BitVec v :=
+  if h : w ≤ v then
+    zeroExtend' h x
+  else
+    .ofNat v x.toNat
+
+/--
+Truncate the high bits of bitvector `x` of length `w`, resulting in a vector of length `v`.
+If `v > w` then it zero-extends the vector instead.
+-/
+abbrev truncate := @zeroExtend
+
+/--
+Sign extend a vector of length `w`, extending with `i` additional copies of the most significant
+bit in `x`. If `x` is an empty vector, then the sign is treated as zero.
+
+SMT-Lib name: `sign_extend`.
+-/
+def signExtend (v : Nat) (x : BitVec w) : BitVec v := .ofInt v x.toInt
+
+end cast
+
+section bitwise
+
+/--
+Bitwise AND for bit vectors.
+
+```lean
+0b1010#4 &&& 0b0110#4 = 0b0010#4
+```
+
+SMT-Lib name: `bvand`.
+-/
+protected def and (x y : BitVec n) : BitVec n :=
+  (x.toNat &&& y.toNat)#'(Nat.and_lt_two_pow x.toNat y.isLt)
+instance : AndOp (BitVec w) := ⟨.and⟩
+
+/--
+Bitwise OR for bit vectors.
+
+```lean
+0b1010#4 ||| 0b0110#4 = 0b1110#4
+```
+
+SMT-Lib name: `bvor`.
+-/
+protected def or (x y : BitVec n) : BitVec n :=
+  (x.toNat ||| y.toNat)#'(Nat.or_lt_two_pow x.isLt y.isLt)
+instance : OrOp (BitVec w) := ⟨.or⟩
+
+/--
+ Bitwise XOR for bit vectors.
+
+```lean
+0b1010#4 ^^^ 0b0110#4 = 0b1100#4
+```
+
+SMT-Lib name: `bvxor`.
+-/
+protected def xor (x y : BitVec n) : BitVec n :=
+  (x.toNat ^^^ y.toNat)#'(Nat.xor_lt_two_pow x.isLt y.isLt)
+instance : Xor (BitVec w) := ⟨.xor⟩
+
+/--
+Bitwise NOT for bit vectors.
+
+```lean
+~~~(0b0101#4) == 0b1010
+```
+SMT-Lib name: `bvnot`.
+-/
+protected def not (x : BitVec n) : BitVec n := allOnes n ^^^ x
+instance : Complement (BitVec w) := ⟨.not⟩
+
+/--
+Left shift for bit vectors. The low bits are filled with zeros. As a numeric operation, this is
+equivalent to `a * 2^s`, modulo `2^n`.
+
+SMT-Lib name: `bvshl` except this operator uses a `Nat` shift value.
+-/
+protected def shiftLeft (a : BitVec n) (s : Nat) : BitVec n := (a.toNat <<< s)#n
+instance : HShiftLeft (BitVec w) Nat (BitVec w) := ⟨.shiftLeft⟩
+
+/--
+(Logical) right shift for bit vectors. The high bits are filled with zeros.
+As a numeric operation, this is equivalent to `a / 2^s`, rounding down.
+
+SMT-Lib name: `bvlshr` except this operator uses a `Nat` shift value.
+-/
+def ushiftRight (a : BitVec n) (s : Nat) : BitVec n :=
+  (a.toNat >>> s)#'(by
+  let ⟨a, lt⟩ := a
+  simp only [BitVec.toNat, Nat.shiftRight_eq_div_pow, Nat.div_lt_iff_lt_mul (Nat.two_pow_pos s)]
+  rw [←Nat.mul_one a]
+  exact Nat.mul_lt_mul_of_lt_of_le' lt (Nat.two_pow_pos s) (Nat.le_refl 1))
+
+instance : HShiftRight (BitVec w) Nat (BitVec w) := ⟨.ushiftRight⟩
+
+/--
+Arithmetic right shift for bit vectors. The high bits are filled with the
+most-significant bit.
+As a numeric operation, this is equivalent to `a.toInt >>> s`.
+
+SMT-Lib name: `bvashr` except this operator uses a `Nat` shift value.
+-/
+def sshiftRight (a : BitVec n) (s : Nat) : BitVec n := .ofInt n (a.toInt >>> s)
+
+instance {n} : HShiftLeft  (BitVec m) (BitVec n) (BitVec m) := ⟨fun x y => x <<< y.toNat⟩
+instance {n} : HShiftRight (BitVec m) (BitVec n) (BitVec m) := ⟨fun x y => x >>> y.toNat⟩
+
+/--
+Rotate left for bit vectors. All the bits of `x` are shifted to higher positions, with the top `n`
+bits wrapping around to fill the low bits.
+
+```lean
+rotateLeft  0b0011#4 3 = 0b1001
+```
+SMT-Lib name: `rotate_left` except this operator uses a `Nat` shift amount.
+-/
+def rotateLeft (x : BitVec w) (n : Nat) : BitVec w := x <<< n ||| x >>> (w - n)
+
+/--
+Rotate right for bit vectors. All the bits of `x` are shifted to lower positions, with the
+bottom `n` bits wrapping around to fill the high bits.
+
+```lean
+rotateRight 0b01001#5 1 = 0b10100
+```
+SMT-Lib name: `rotate_right` except this operator uses a `Nat` shift amount.
+-/
+def rotateRight (x : BitVec w) (n : Nat) : BitVec w := x >>> n ||| x <<< (w - n)
+
+/--
+Concatenation of bitvectors. This uses the "big endian" convention that the more significant
+input is on the left, so `0xAB#8 ++ 0xCD#8 = 0xABCD#16`.
+
+SMT-Lib name: `concat`.
+-/
+def append (msbs : BitVec n) (lsbs : BitVec m) : BitVec (n+m) :=
+  shiftLeftZeroExtend msbs m ||| zeroExtend' (Nat.le_add_left m n) lsbs
+
+instance : HAppend (BitVec w) (BitVec v) (BitVec (w + v)) := ⟨.append⟩
+
+-- TODO: write this using multiplication
+/-- `replicate i x` concatenates `i` copies of `x` into a new vector of length `w*i`. -/
+def replicate : (i : Nat) → BitVec w → BitVec (w*i)
+  | 0,   _ => 0
+  | n+1, x =>
+    have hEq : w + w*n = w*(n + 1) := by
+      rw [Nat.mul_add, Nat.add_comm, Nat.mul_one]
+    hEq ▸ (x ++ replicate n x)
+
+/-!
+### Cons and Concat
+We give special names to the operations of adding a single bit to either end of a bitvector.
+We follow the precedent of `Vector.cons`/`Vector.concat` both for the name, and for the decision
+to have the resulting size be `n + 1` for both operations (rather than `1 + n`, which would be the
+result of appending a single bit to the front in the naive implementation).
+-/
+
+/-- Append a single bit to the end of a bitvector, using big endian order (see `append`).
+    That is, the new bit is the least significant bit. -/
+def concat {n} (msbs : BitVec n) (lsb : Bool) : BitVec (n+1) := msbs ++ (ofBool lsb)
+
+/-- Prepend a single bit to the front of a bitvector, using big endian order (see `append`).
+    That is, the new bit is the most significant bit. -/
+def cons {n} (msb : Bool) (lsbs : BitVec n) : BitVec (n+1) :=
+  ((ofBool msb) ++ lsbs).cast (Nat.add_comm ..)
+
+theorem append_ofBool (msbs : BitVec w) (lsb : Bool) :
+    msbs ++ ofBool lsb = concat msbs lsb :=
+  rfl
+
+theorem ofBool_append (msb : Bool) (lsbs : BitVec w) :
+    ofBool msb ++ lsbs = (cons msb lsbs).cast (Nat.add_comm ..) :=
+  rfl
+
+end bitwise
+
+section normalization_eqs
+/-! We add simp-lemmas that rewrite bitvector operations into the equivalent notation -/
+@[simp] theorem append_eq (x : BitVec w) (y : BitVec v)   : BitVec.append x y = x ++ y        := rfl
+@[simp] theorem shiftLeft_eq (x : BitVec w) (n : Nat)     : BitVec.shiftLeft x n = x <<< n    := rfl
+@[simp] theorem ushiftRight_eq (x : BitVec w) (n : Nat)   : BitVec.ushiftRight x n = x >>> n  := rfl
+@[simp] theorem not_eq (x : BitVec w)                     : BitVec.not x = ~~~x               := rfl
+@[simp] theorem and_eq (x y : BitVec w)                   : BitVec.and x y = x &&& y          := rfl
+@[simp] theorem or_eq (x y : BitVec w)                    : BitVec.or x y = x ||| y           := rfl
+@[simp] theorem xor_eq (x y : BitVec w)                   : BitVec.xor x y = x ^^^ y          := rfl
+@[simp] theorem neg_eq (x : BitVec w)                     : BitVec.neg x = -x                 := rfl
+@[simp] theorem add_eq (x y : BitVec w)                   : BitVec.add x y = x + y            := rfl
+@[simp] theorem sub_eq (x y : BitVec w)                   : BitVec.sub x y = x - y            := rfl
+@[simp] theorem mul_eq (x y : BitVec w)                   : BitVec.mul x y = x * y            := rfl
+@[simp] theorem zero_eq                                   : BitVec.zero n = 0#n               := rfl
+end normalization_eqs
+
+/-- Converts a list of `Bool`s to a big-endian `BitVec`. -/
+def ofBoolListBE : (bs : List Bool) → BitVec bs.length
+| [] => 0#0
+| b :: bs => cons b (ofBoolListBE bs)
+
+/-- Converts a list of `Bool`s to a little-endian `BitVec`. -/
+def ofBoolListLE : (bs : List Bool) → BitVec bs.length
+| [] => 0#0
+| b :: bs => concat (ofBoolListLE bs) b
+
+end BitVec

src/Init/Data/BitVec/Bitblast.lean

@@ -0,0 +1,162 @@
+/-
+Copyright (c) 2024 Lean FRO, LLC. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Harun Khan, Abdalrhman M Mohamed, Joe Hendrix
+-/
+prelude
+import Init.Data.BitVec.Folds
+import Init.Data.Nat.Mod
+
+/-!
+# Bitblasting of bitvectors
+
+This module provides theorems for showing the equivalence between BitVec operations using
+the `Fin 2^n` representation and Boolean vectors.  It is still under development, but
+intended to provide a path for converting SAT and SMT solver proofs about BitVectors
+as vectors of bits into proofs about Lean `BitVec` values.
+
+The module is named for the bit-blasting operation in an SMT solver that converts bitvector
+expressions into expressions about individual bits in each vector.
+
+## Main results
+* `x + y : BitVec w` is `(adc x y false).2`.
+
+
+## Future work
+All other operations are to be PR'ed later and are already proved in
+https://github.com/mhk119/lean-smt/blob/bitvec/Smt/Data/Bitwise.lean.
+
+-/
+
+open Nat Bool
+
+namespace Bool
+
+/-- At least two out of three booleans are true. -/
+abbrev atLeastTwo (a b c : Bool) : Bool := a && b || a && c || b && c
+
+@[simp] theorem atLeastTwo_false_left  : atLeastTwo false b c = (b && c) := by simp [atLeastTwo]
+@[simp] theorem atLeastTwo_false_mid   : atLeastTwo a false c = (a && c) := by simp [atLeastTwo]
+@[simp] theorem atLeastTwo_false_right : atLeastTwo a b false = (a && b) := by simp [atLeastTwo]
+@[simp] theorem atLeastTwo_true_left   : atLeastTwo true b c  = (b || c) := by cases b <;> cases c <;> simp [atLeastTwo]
+@[simp] theorem atLeastTwo_true_mid    : atLeastTwo a true c  = (a || c) := by cases a <;> cases c <;> simp [atLeastTwo]
+@[simp] theorem atLeastTwo_true_right  : atLeastTwo a b true  = (a || b) := by cases a <;> cases b <;> simp [atLeastTwo]
+
+end Bool
+
+/-! ### Preliminaries -/
+
+namespace BitVec
+
+private theorem testBit_limit {x i : Nat} (x_lt_succ : x < 2^(i+1)) :
+    testBit x i = decide (x ≥ 2^i) := by
+  cases xi : testBit x i with
+  | true =>
+    simp [testBit_implies_ge xi]
+  | false =>
+    simp
+    cases Nat.lt_or_ge x (2^i) with
+    | inl x_lt =>
+      exact x_lt
+    | inr x_ge =>
+      have ⟨j, ⟨j_ge, jp⟩⟩  := ge_two_pow_implies_high_bit_true x_ge
+      cases Nat.lt_or_eq_of_le j_ge with
+      | inr x_eq =>
+        simp [x_eq, jp] at xi
+      | inl x_lt =>
+        exfalso
+        apply Nat.lt_irrefl
+        calc x < 2^(i+1) := x_lt_succ
+             _ ≤ 2 ^ j := Nat.pow_le_pow_of_le_right Nat.zero_lt_two x_lt
+             _ ≤ x := testBit_implies_ge jp
+
+private theorem mod_two_pow_succ (x i : Nat) :
+    x % 2^(i+1) = 2^i*(x.testBit i).toNat + x % (2 ^ i):= by
+  rw [Nat.mod_pow_succ, Nat.add_comm, Nat.toNat_testBit]
+
+private theorem mod_two_pow_add_mod_two_pow_add_bool_lt_two_pow_succ
+     (x y i : Nat) (c : Bool) : x % 2^i + (y % 2^i + c.toNat) < 2^(i+1) := by
+  have : c.toNat ≤ 1 := Bool.toNat_le c
+  rw [Nat.pow_succ]
+  omega
+
+/-! ### Addition -/
+
+/-- carry i x y c returns true if the `i` carry bit is true when computing `x + y + c`. -/
+def carry (i : Nat) (x y : BitVec w) (c : Bool) : Bool :=
+  decide (x.toNat % 2^i + y.toNat % 2^i + c.toNat ≥ 2^i)
+
+@[simp] theorem carry_zero : carry 0 x y c = c := by
+  cases c <;> simp [carry, mod_one]
+
+theorem carry_succ (i : Nat) (x y : BitVec w) (c : Bool) :
+    carry (i+1) x y c = atLeastTwo (x.getLsb i) (y.getLsb i) (carry i x y c) := by
+  simp only [carry, mod_two_pow_succ, atLeastTwo, getLsb]
+  simp only [Nat.pow_succ']
+  have sum_bnd : x.toNat%2^i + (y.toNat%2^i + c.toNat) < 2*2^i := by
+    simp only [← Nat.pow_succ']
+    exact mod_two_pow_add_mod_two_pow_add_bool_lt_two_pow_succ ..
+  cases x.toNat.testBit i <;> cases y.toNat.testBit i <;> (simp; omega)
+
+/-- Carry function for bitwise addition. -/
+def adcb (x y c : Bool) : Bool × Bool := (atLeastTwo x y c, Bool.xor x (Bool.xor y c))
+
+/-- Bitwise addition implemented via a ripple carry adder. -/
+def adc (x y : BitVec w) : Bool → Bool × BitVec w :=
+  iunfoldr fun (i : Fin w) c => adcb (x.getLsb i) (y.getLsb i) c
+
+theorem getLsb_add_add_bool {i : Nat} (i_lt : i < w) (x y : BitVec w) (c : Bool) :
+    getLsb (x + y + zeroExtend w (ofBool c)) i =
+      Bool.xor (getLsb x i) (Bool.xor (getLsb y i) (carry i x y c)) := by
+  let ⟨x, x_lt⟩ := x
+  let ⟨y, y_lt⟩ := y
+  simp only [getLsb, toNat_add, toNat_zeroExtend, i_lt, toNat_ofFin, toNat_ofBool,
+    Nat.mod_add_mod, Nat.add_mod_mod]
+  apply Eq.trans
+  rw [← Nat.div_add_mod x (2^i), ← Nat.div_add_mod y (2^i)]
+  simp only
+    [ Nat.testBit_mod_two_pow,
+      Nat.testBit_mul_two_pow_add_eq,
+      i_lt,
+      decide_True,
+      Bool.true_and,
+      Nat.add_assoc,
+      Nat.add_left_comm (_%_) (_ * _) _,
+      testBit_limit (mod_two_pow_add_mod_two_pow_add_bool_lt_two_pow_succ x y i c)
+    ]
+  simp [testBit_to_div_mod, carry, Nat.add_assoc]
+
+theorem getLsb_add {i : Nat} (i_lt : i < w) (x y : BitVec w) :
+    getLsb (x + y) i =
+      Bool.xor (getLsb x i) (Bool.xor (getLsb y i) (carry i x y false)) := by
+  simpa using getLsb_add_add_bool i_lt x y false
+
+theorem adc_spec (x y : BitVec w) (c : Bool) :
+    adc x y c = (carry w x y c, x + y + zeroExtend w (ofBool c)) := by
+  simp only [adc]
+  apply iunfoldr_replace
+          (fun i => carry i x y c)
+          (x + y + zeroExtend w (ofBool c))
+          c
+  case init =>
+    simp [carry, Nat.mod_one]
+    cases c <;> rfl
+  case step =>
+    simp [adcb, Prod.mk.injEq, carry_succ, getLsb_add_add_bool]
+
+theorem add_eq_adc (w : Nat) (x y : BitVec w) : x + y = (adc x y false).snd := by
+  simp [adc_spec]
+
+/-! ### add -/
+
+/-- Adding a bitvector to its own complement yields the all ones bitpattern -/
+@[simp] theorem add_not_self (x : BitVec w) : x + ~~~x = allOnes w := by
+  rw [add_eq_adc, adc, iunfoldr_replace (fun _ => false) (allOnes w)]
+  · rfl
+  · simp [adcb, atLeastTwo]
+
+/-- Subtracting `x` from the all ones bitvector is equivalent to taking its complement -/
+theorem allOnes_sub_eq_not (x : BitVec w) : allOnes w - x = ~~~x := by
+  rw [← add_not_self x, BitVec.add_comm, add_sub_cancel]
+
+end BitVec

src/Init/Data/BitVec/Folds.lean

@@ -0,0 +1,61 @@
+/-
+Copyright (c) 2023 Lean FRO, LLC. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Joe Hendrix
+-/
+prelude
+import Init.Data.BitVec.Lemmas
+import Init.Data.Nat.Lemmas
+import Init.Data.Fin.Iterate
+
+namespace BitVec
+
+/--
+iunfoldr is an iterative operation that applies a function `f` repeatedly.
+
+It produces a sequence of state values `[s_0, s_1 .. s_w]` and a bitvector
+`v` where `f i s_i = (s_{i+1}, b_i)` and `b_i` is bit `i`th least-significant bit
+in `v` (e.g., `getLsb v i = b_i`).
+
+Theorems involving `iunfoldr` can be eliminated using `iunfoldr_replace` below.
+-/
+def iunfoldr (f : Fin w -> α → α × Bool) (s : α) : α × BitVec w :=
+  Fin.hIterate (fun i => α × BitVec i) (s, nil) fun i q =>
+    (fun p => ⟨p.fst, cons p.snd q.snd⟩) (f i q.fst)
+
+theorem iunfoldr.fst_eq
+    {f : Fin w → α → α × Bool} (state : Nat → α) (s : α)
+    (init : s = state 0)
+    (ind : ∀(i : Fin w), (f i (state i.val)).fst = state (i.val+1)) :
+    (iunfoldr f s).fst = state w := by
+  unfold iunfoldr
+  apply Fin.hIterate_elim (fun i (p : α × BitVec i) => p.fst = state i)
+  case init =>
+    exact init
+  case step =>
+    intro i ⟨s, v⟩ p
+    simp_all [ind i]
+
+private theorem iunfoldr.eq_test
+    {f : Fin w → α → α × Bool} (state : Nat → α) (value : BitVec w) (a : α)
+    (init : state 0 = a)
+    (step : ∀(i : Fin w), f i (state i.val) = (state (i.val+1), value.getLsb i.val)) :
+    iunfoldr f a = (state w, BitVec.truncate w value) := by
+  apply Fin.hIterate_eq (fun i => ((state i, BitVec.truncate i value) : α × BitVec i))
+  case init =>
+    simp only [init, eq_nil]
+  case step =>
+    intro i
+    simp_all [truncate_succ]
+
+/--
+Correctness theorem for `iunfoldr`.
+-/
+theorem iunfoldr_replace
+    {f : Fin w → α → α × Bool} (state : Nat → α) (value : BitVec w) (a : α)
+    (init : state 0 = a)
+    (step : ∀(i : Fin w), f i (state i.val) = (state (i.val+1), value.getLsb i.val)) :
+    iunfoldr f a = (state w, value) := by
+  simp [iunfoldr.eq_test state value a init step]
+
+end BitVec

src/Init/Data/BitVec/Lemmas.lean

@@ -0,0 +1,974 @@
+/-
+Copyright (c) 2023 Lean FRO, LLC. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Joe Hendrix
+-/
+prelude
+import Init.Data.Bool
+import Init.Data.BitVec.Basic
+import Init.Data.Fin.Lemmas
+import Init.Data.Nat.Lemmas
+
+namespace BitVec
+
+/--
+This normalized a bitvec using `ofFin` to `ofNat`.
+-/
+theorem ofFin_eq_ofNat : @BitVec.ofFin w (Fin.mk x lt) = BitVec.ofNat w x := by
+  simp only [BitVec.ofNat, Fin.ofNat', lt, Nat.mod_eq_of_lt]
+
+/-- Prove equality of bitvectors in terms of nat operations. -/
+theorem eq_of_toNat_eq {n} : ∀ {i j : BitVec n}, i.toNat = j.toNat → i = j
+  | ⟨_, _⟩, ⟨_, _⟩, rfl => rfl
+
+@[simp] theorem val_toFin (x : BitVec w) : x.toFin.val = x.toNat := rfl
+
+@[bv_toNat] theorem toNat_eq (x y : BitVec n) : x = y ↔ x.toNat = y.toNat :=
+  Iff.intro (congrArg BitVec.toNat) eq_of_toNat_eq
+
+@[bv_toNat] theorem toNat_ne (x y : BitVec n) : x ≠ y ↔ x.toNat ≠ y.toNat := by
+  rw [Ne, toNat_eq]
+
+theorem testBit_toNat (x : BitVec w) : x.toNat.testBit i = x.getLsb i := rfl
+
+@[simp] theorem getLsb_ofFin (x : Fin (2^n)) (i : Nat) :
+  getLsb (BitVec.ofFin x) i = x.val.testBit i := rfl
+
+@[simp] theorem getLsb_ge (x : BitVec w) (i : Nat) (ge : w ≤ i) : getLsb x i = false := by
+  let ⟨x, x_lt⟩ := x
+  simp
+  apply Nat.testBit_lt_two_pow
+  have p : 2^w ≤ 2^i := Nat.pow_le_pow_of_le_right (by omega) ge
+  omega
+
+@[simp] theorem getMsb_ge (x : BitVec w) (i : Nat) (ge : w ≤ i) : getMsb x i = false := by
+  rw [getMsb]
+  simp only [Bool.and_eq_false_imp, decide_eq_true_eq]
+  omega
+
+theorem lt_of_getLsb (x : BitVec w) (i : Nat) : getLsb x i = true → i < w := by
+  if h : i < w then
+    simp [h]
+  else
+    simp [Nat.ge_of_not_lt h]
+
+theorem lt_of_getMsb (x : BitVec w) (i : Nat) : getMsb x i = true → i < w := by
+  if h : i < w then
+    simp [h]
+  else
+    simp [Nat.ge_of_not_lt h]
+
+theorem getMsb_eq_getLsb (x : BitVec w) (i : Nat) : x.getMsb i = (decide (i < w) && x.getLsb (w - 1 - i)) := by
+  rw [getMsb]
+
+theorem getLsb_eq_getMsb (x : BitVec w) (i : Nat) : x.getLsb i = (decide (i < w) && x.getMsb (w - 1 - i)) := by
+  rw [getMsb]
+  by_cases h₁ : i < w <;> by_cases h₂ : w - 1 - i < w <;>
+    simp only [h₁, h₂] <;> simp only [decide_True, decide_False, Bool.false_and, Bool.and_false, Bool.true_and, Bool.and_true]
+  · congr
+    omega
+  all_goals
+    apply getLsb_ge
+    omega
+
+-- We choose `eq_of_getLsb_eq` as the `@[ext]` theorem for `BitVec`
+-- somewhat arbitrarily over `eq_of_getMsg_eq`.
+@[ext] theorem eq_of_getLsb_eq {x y : BitVec w}
+    (pred : ∀(i : Fin w), x.getLsb i.val = y.getLsb i.val) : x = y := by
+  apply eq_of_toNat_eq
+  apply Nat.eq_of_testBit_eq
+  intro i
+  if i_lt : i < w then
+    exact pred ⟨i, i_lt⟩
+  else
+    have p : i ≥ w := Nat.le_of_not_gt i_lt
+    simp [testBit_toNat, getLsb_ge _ _ p]
+
+theorem eq_of_getMsb_eq {x y : BitVec w}
+    (pred : ∀(i : Fin w), x.getMsb i = y.getMsb i.val) : x = y := by
+  simp only [getMsb] at pred
+  apply eq_of_getLsb_eq
+  intro ⟨i, i_lt⟩
+  if w_zero : w = 0 then
+    simp [w_zero]
+  else
+    have w_pos := Nat.pos_of_ne_zero w_zero
+    have r : i ≤ w - 1 := by
+      simp [Nat.le_sub_iff_add_le w_pos]
+      exact i_lt
+    have q_lt : w - 1 - i < w := by
+      simp only [Nat.sub_sub]
+      apply Nat.sub_lt w_pos
+      simp [Nat.succ_add]
+    have q := pred ⟨w - 1 - i, q_lt⟩
+    simpa [q_lt, Nat.sub_sub_self, r] using q
+
+@[simp] theorem of_length_zero {x : BitVec 0} : x = 0#0 := by ext; simp
+
+theorem eq_of_toFin_eq : ∀ {x y : BitVec w}, x.toFin = y.toFin → x = y
+  | ⟨_, _⟩, ⟨_, _⟩, rfl => rfl
+
+@[simp] theorem toNat_ofBool (b : Bool) : (ofBool b).toNat = b.toNat := by
+  cases b <;> rfl
+
+@[simp] theorem msb_ofBool (b : Bool) : (ofBool b).msb = b := by
+  cases b <;> simp [BitVec.msb]
+
+theorem ofNat_one (n : Nat) : BitVec.ofNat 1 n = BitVec.ofBool (n % 2 = 1) :=  by
+  rcases (Nat.mod_two_eq_zero_or_one n) with h | h <;> simp [h, BitVec.ofNat, Fin.ofNat']
+
+theorem ofBool_eq_iff_eq : ∀(b b' : Bool), BitVec.ofBool b = BitVec.ofBool b' ↔ b = b' := by
+  decide
+
+@[simp] theorem not_ofBool : ~~~ (ofBool b) = ofBool (!b) := by cases b <;> rfl
+
+@[simp, bv_toNat] theorem toNat_ofFin (x : Fin (2^n)) : (BitVec.ofFin x).toNat = x.val := rfl
+
+@[simp] theorem toNat_ofNatLt (x : Nat) (p : x < 2^w) : (x#'p).toNat = x := rfl
+
+@[simp] theorem getLsb_ofNatLt {n : Nat} (x : Nat) (lt : x < 2^n) (i : Nat) :
+  getLsb (x#'lt) i = x.testBit i := by
+  simp [getLsb, BitVec.ofNatLt]
+
+@[simp, bv_toNat] theorem toNat_ofNat (x w : Nat) : (x#w).toNat = x % 2^w := by
+  simp [BitVec.toNat, BitVec.ofNat, Fin.ofNat']
+
+-- Remark: we don't use `[simp]` here because simproc` subsumes it for literals.
+-- If `x` and `n` are not literals, applying this theorem eagerly may not be a good idea.
+theorem getLsb_ofNat (n : Nat) (x : Nat) (i : Nat) :
+  getLsb (x#n) i = (i < n && x.testBit i) := by
+  simp [getLsb, BitVec.ofNat, Fin.val_ofNat']
+
+@[simp, deprecated toNat_ofNat] theorem toNat_zero (n : Nat) : (0#n).toNat = 0 := by trivial
+
+@[simp] theorem getLsb_zero : (0#w).getLsb i = false := by simp [getLsb]
+
+@[simp] theorem getMsb_zero : (0#w).getMsb i = false := by simp [getMsb]
+
+@[simp] theorem toNat_mod_cancel (x : BitVec n) : x.toNat % (2^n) = x.toNat :=
+  Nat.mod_eq_of_lt x.isLt
+
+private theorem lt_two_pow_of_le {x m n : Nat} (lt : x < 2 ^ m) (le : m ≤ n) : x < 2 ^ n :=
+  Nat.lt_of_lt_of_le lt (Nat.pow_le_pow_of_le_right (by trivial : 0 < 2) le)
+
+/-! ### msb -/
+
+@[simp] theorem msb_zero : (0#w).msb = false := by simp [BitVec.msb, getMsb]
+
+theorem msb_eq_getLsb_last (x : BitVec w) :
+    x.msb = x.getLsb (w - 1) := by
+  simp [BitVec.msb, getMsb, getLsb]
+  rcases w  with rfl | w
+  · simp [BitVec.eq_nil x]
+  · simp
+
+@[bv_toNat] theorem getLsb_last (x : BitVec w) :
+    x.getLsb (w-1) = decide (2 ^ (w-1) ≤ x.toNat) := by
+  rcases w with rfl | w
+  · simp
+  · simp only [Nat.zero_lt_succ, decide_True, getLsb, Nat.testBit, Nat.succ_sub_succ_eq_sub,
+    Nat.sub_zero, Nat.and_one_is_mod, Bool.true_and, Nat.shiftRight_eq_div_pow]
+    rcases (Nat.lt_or_ge (BitVec.toNat x) (2 ^ w)) with h | h
+    · simp [Nat.div_eq_of_lt h, h]
+    · simp only [h]
+      rw [Nat.div_eq_sub_div (Nat.two_pow_pos w) h, Nat.div_eq_of_lt]
+      · decide
+      · have : BitVec.toNat x < 2^w + 2^w := by simpa [Nat.pow_succ, Nat.mul_two] using x.isLt
+        omega
+
+@[bv_toNat] theorem getLsb_succ_last (x : BitVec (w + 1)) :
+    x.getLsb w = decide (2 ^ w ≤ x.toNat) := getLsb_last x
+
+@[bv_toNat] theorem msb_eq_decide (x : BitVec w) : BitVec.msb x = decide (2 ^ (w-1) ≤ x.toNat) := by
+  simp [msb_eq_getLsb_last, getLsb_last]
+
+theorem toNat_ge_of_msb_true {x : BitVec n} (p : BitVec.msb x = true) : x.toNat ≥ 2^(n-1) := by
+  match n with
+  | 0 =>
+    simp [BitVec.msb, BitVec.getMsb] at p
+  | n + 1 =>
+    simp [BitVec.msb_eq_decide] at p
+    simp only [Nat.add_sub_cancel]
+    exact p
+
+/-! ### cast -/
+
+@[simp, bv_toNat] theorem toNat_cast (h : w = v) (x : BitVec w) : (cast h x).toNat = x.toNat := rfl
+@[simp] theorem toFin_cast (h : w = v) (x : BitVec w) :
+    (cast h x).toFin = x.toFin.cast (by rw [h]) :=
+  rfl
+
+@[simp] theorem getLsb_cast (h : w = v) (x : BitVec w) : (cast h x).getLsb i = x.getLsb i := by
+  subst h; simp
+
+@[simp] theorem getMsb_cast (h : w = v) (x : BitVec w) : (cast h x).getMsb i = x.getMsb i := by
+  subst h; simp
+@[simp] theorem msb_cast (h : w = v) (x : BitVec w) : (cast h x).msb = x.msb := by
+  simp [BitVec.msb]
+
+/-! ### toInt/ofInt -/
+
+/-- Prove equality of bitvectors in terms of nat operations. -/
+theorem toInt_eq_toNat_cond (i : BitVec n) :
+    i.toInt =
+      if 2*i.toNat < 2^n then
+        (i.toNat : Int)
+      else
+        (i.toNat : Int) - (2^n : Nat) := by
+  unfold BitVec.toInt
+  split <;> omega
+
+theorem toInt_eq_toNat_bmod (x : BitVec n) : x.toInt = Int.bmod x.toNat (2^n) := by
+  simp only [toInt_eq_toNat_cond]
+  split
+  case inl g =>
+    rw [Int.bmod_pos] <;> simp only [←Int.ofNat_emod, toNat_mod_cancel]
+    omega
+  case inr g =>
+    rw [Int.bmod_neg] <;> simp only [←Int.ofNat_emod, toNat_mod_cancel]
+    omega
+
+/-- Prove equality of bitvectors in terms of nat operations. -/
+theorem eq_of_toInt_eq {i j : BitVec n} : i.toInt = j.toInt → i = j := by
+  intro eq
+  simp [toInt_eq_toNat_cond] at eq
+  apply eq_of_toNat_eq
+  revert eq
+  have _ilt := i.isLt
+  have _jlt := j.isLt
+  split <;> split <;> omega
+
+@[simp] theorem toNat_ofInt {n : Nat} (i : Int) :
+  (BitVec.ofInt n i).toNat = (i % (2^n : Nat)).toNat := by
+  unfold BitVec.ofInt
+  simp
+
+theorem toInt_ofNat {n : Nat} (x : Nat) :
+  (BitVec.ofNat n x).toInt = (x : Int).bmod (2^n) := by
+  simp [toInt_eq_toNat_bmod]
+
+@[simp] theorem toInt_ofInt {n : Nat} (i : Int) :
+  (BitVec.ofInt n i).toInt = i.bmod (2^n) := by
+  have _ := Nat.two_pow_pos n
+  have p : 0 ≤ i % (2^n : Nat) := by omega
+  simp [toInt_eq_toNat_bmod, Int.toNat_of_nonneg p]
+
+/-! ### zeroExtend and truncate -/
+
+@[simp, bv_toNat] theorem toNat_zeroExtend' {m n : Nat} (p : m ≤ n) (x : BitVec m) :
+    (zeroExtend' p x).toNat = x.toNat := by
+  unfold zeroExtend'
+  simp [p, x.isLt, Nat.mod_eq_of_lt]
+
+@[bv_toNat] theorem toNat_zeroExtend (i : Nat) (x : BitVec n) :
+    BitVec.toNat (zeroExtend i x) = x.toNat % 2^i := by
+  let ⟨x, lt_n⟩ := x
+  simp only [zeroExtend]
+  if n_le_i : n ≤ i then
+    have x_lt_two_i : x < 2 ^ i := lt_two_pow_of_le lt_n n_le_i
+    simp [n_le_i, Nat.mod_eq_of_lt, x_lt_two_i]
+  else
+    simp [n_le_i, toNat_ofNat]
+
+theorem zeroExtend'_eq {x : BitVec w} (h : w ≤ v) : x.zeroExtend' h = x.zeroExtend v := by
+  apply eq_of_toNat_eq
+  rw [toNat_zeroExtend, toNat_zeroExtend']
+  rw [Nat.mod_eq_of_lt]
+  exact Nat.lt_of_lt_of_le x.isLt (Nat.pow_le_pow_right (Nat.zero_lt_two) h)
+
+@[simp, bv_toNat] theorem toNat_truncate (x : BitVec n) : (truncate i x).toNat = x.toNat % 2^i :=
+  toNat_zeroExtend i x
+
+@[simp] theorem zeroExtend_eq (x : BitVec n) : zeroExtend n x = x := by
+  apply eq_of_toNat_eq
+  let ⟨x, lt_n⟩ := x
+  simp [truncate, zeroExtend]
+
+@[simp] theorem zeroExtend_zero (m n : Nat) : zeroExtend m (0#n) = 0#m := by
+  apply eq_of_toNat_eq
+  simp [toNat_zeroExtend]
+
+@[simp] theorem truncate_eq (x : BitVec n) : truncate n x = x := zeroExtend_eq x
+
+@[simp] theorem ofNat_toNat (m : Nat) (x : BitVec n) : x.toNat#m = truncate m x := by
+  apply eq_of_toNat_eq
+  simp
+
+/-- Moves one-sided left toNat equality to BitVec equality. -/
+theorem toNat_eq_nat (x : BitVec w) (y : Nat)
+  : (x.toNat = y) ↔ (y < 2^w ∧ (x = y#w)) := by
+  apply Iff.intro
+  · intro eq
+    simp at eq
+    have lt := x.isLt
+    simp [eq] at lt
+    simp [←eq, lt, x.isLt]
+  · intro eq
+    simp [Nat.mod_eq_of_lt, eq]
+
+/-- Moves one-sided right toNat equality to BitVec equality. -/
+theorem nat_eq_toNat (x : BitVec w) (y : Nat)
+  : (y = x.toNat) ↔ (y < 2^w ∧ (x = y#w)) := by
+  rw [@eq_comm _ _ x.toNat]
+  apply toNat_eq_nat
+
+@[simp] theorem getLsb_zeroExtend' (ge : m ≥ n) (x : BitVec n) (i : Nat) :
+    getLsb (zeroExtend' ge x) i = getLsb x i := by
+  simp [getLsb, toNat_zeroExtend']
+
+@[simp] theorem getMsb_zeroExtend' (ge : m ≥ n) (x : BitVec n) (i : Nat) :
+    getMsb (zeroExtend' ge x) i = (decide (i ≥ m - n) && getMsb x (i - (m - n))) := by
+  simp only [getMsb, getLsb_zeroExtend', gt_iff_lt]
+  by_cases h₁ : decide (i < m) <;> by_cases h₂ : decide (i ≥ m - n) <;> by_cases h₃ : decide (i - (m - n) < n) <;>
+    by_cases h₄ : n - 1 - (i - (m - n)) = m - 1 - i
+  all_goals
+    simp only [h₁, h₂, h₃, h₄]
+    simp_all only [ge_iff_le, decide_eq_true_eq, Nat.not_le, Nat.not_lt, Bool.true_and,
+      Bool.false_and, Bool.and_self] <;>
+    (try apply getLsb_ge) <;>
+    (try apply (getLsb_ge _ _ _).symm) <;>
+    omega
+
+@[simp] theorem getLsb_zeroExtend (m : Nat) (x : BitVec n) (i : Nat) :
+    getLsb (zeroExtend m x) i = (decide (i < m) && getLsb x i) := by
+  simp [getLsb, toNat_zeroExtend, Nat.testBit_mod_two_pow]
+
+@[simp] theorem getMsb_zeroExtend_add {x : BitVec w} (h : k ≤ i) :
+    (x.zeroExtend (w + k)).getMsb i = x.getMsb (i - k) := by
+  by_cases h : w = 0
+  · subst h; simp
+  simp only [getMsb, getLsb_zeroExtend]
+  by_cases h₁ : i < w + k <;> by_cases h₂ : i - k < w <;> by_cases h₃ : w + k - 1 - i < w + k
+    <;> simp [h₁, h₂, h₃]
+  · congr 1
+    omega
+  all_goals (first | apply getLsb_ge | apply Eq.symm; apply getLsb_ge)
+    <;> omega
+
+@[simp] theorem getLsb_truncate (m : Nat) (x : BitVec n) (i : Nat) :
+    getLsb (truncate m x) i = (decide (i < m) && getLsb x i) :=
+  getLsb_zeroExtend m x i
+
+theorem msb_truncate (x : BitVec w) : (x.truncate (k + 1)).msb = x.getLsb k := by
+  simp [BitVec.msb, getMsb]
+
+@[simp] theorem zeroExtend_zeroExtend_of_le (x : BitVec w) (h : k ≤ l) :
+    (x.zeroExtend l).zeroExtend k = x.zeroExtend k := by
+  ext i
+  simp only [getLsb_zeroExtend, Fin.is_lt, decide_True, Bool.true_and]
+  have p := lt_of_getLsb x i
+  revert p
+  cases getLsb x i <;> simp; omega
+
+@[simp] theorem truncate_truncate_of_le (x : BitVec w) (h : k ≤ l) :
+    (x.truncate l).truncate k = x.truncate k :=
+  zeroExtend_zeroExtend_of_le x h
+
+@[simp] theorem truncate_cast {h : w = v} : (cast h x).truncate k = x.truncate k := by
+  apply eq_of_getLsb_eq
+  simp
+
+theorem msb_zeroExtend (x : BitVec w) : (x.zeroExtend v).msb = (decide (0 < v) && x.getLsb (v - 1)) := by
+  rw [msb_eq_getLsb_last]
+  simp only [getLsb_zeroExtend]
+  cases getLsb x (v - 1) <;> simp; omega
+
+theorem msb_zeroExtend' (x : BitVec w) (h : w ≤ v) : (x.zeroExtend' h).msb = (decide (0 < v) && x.getLsb (v - 1)) := by
+  rw [zeroExtend'_eq, msb_zeroExtend]
+
+/-! ## extractLsb -/
+
+@[simp]
+protected theorem extractLsb_ofFin {n} (x : Fin (2^n)) (hi lo : Nat) :
+  extractLsb hi lo (@BitVec.ofFin n x) = .ofNat (hi-lo+1) (x.val >>> lo) := rfl
+
+@[simp]
+protected theorem extractLsb_ofNat (x n : Nat) (hi lo : Nat) :
+  extractLsb hi lo x#n = .ofNat (hi - lo + 1) ((x % 2^n) >>> lo) := by
+  apply eq_of_getLsb_eq
+  intro ⟨i, _lt⟩
+  simp [BitVec.ofNat]
+
+@[simp] theorem extractLsb'_toNat (s m : Nat) (x : BitVec n) :
+  (extractLsb' s m x).toNat = (x.toNat >>> s) % 2^m := rfl
+
+@[simp] theorem extractLsb_toNat (hi lo : Nat) (x : BitVec n) :
+  (extractLsb hi lo x).toNat = (x.toNat >>> lo) % 2^(hi-lo+1) := rfl
+
+@[simp] theorem getLsb_extract (hi lo : Nat) (x : BitVec n) (i : Nat) :
+    getLsb (extractLsb hi lo x) i = (i ≤ (hi-lo) && getLsb x (lo+i)) := by
+  unfold getLsb
+  simp [Nat.lt_succ]
+
+/-! ### allOnes -/
+
+@[simp] theorem toNat_allOnes : (allOnes v).toNat = 2^v - 1 := by
+  unfold allOnes
+  simp
+
+@[simp] theorem getLsb_allOnes : (allOnes v).getLsb i = decide (i < v) := by
+  simp [allOnes]
+
+/-! ### or -/
+
+@[simp] theorem toNat_or (x y : BitVec v) :
+    BitVec.toNat (x ||| y) = BitVec.toNat x ||| BitVec.toNat y := rfl
+
+@[simp] theorem toFin_or (x y : BitVec v) :
+    BitVec.toFin (x ||| y) = BitVec.toFin x ||| BitVec.toFin y := by
+  apply Fin.eq_of_val_eq
+  exact (Nat.mod_eq_of_lt <| Nat.or_lt_two_pow x.isLt y.isLt).symm
+
+@[simp] theorem getLsb_or {x y : BitVec v} : (x ||| y).getLsb i = (x.getLsb i || y.getLsb i) := by
+  rw [← testBit_toNat, getLsb, getLsb]
+  simp
+
+@[simp] theorem getMsb_or {x y : BitVec w} : (x ||| y).getMsb i = (x.getMsb i || y.getMsb i) := by
+  simp only [getMsb]
+  by_cases h : i < w <;> simp [h]
+
+@[simp] theorem msb_or {x y : BitVec w} : (x ||| y).msb = (x.msb || y.msb) := by
+  simp [BitVec.msb]
+
+@[simp] theorem truncate_or {x y : BitVec w} :
+    (x ||| y).truncate k = x.truncate k ||| y.truncate k := by
+  ext
+  simp
+
+/-! ### and -/
+
+@[simp] theorem toNat_and (x y : BitVec v) :
+    BitVec.toNat (x &&& y) = BitVec.toNat x &&& BitVec.toNat y := rfl
+
+@[simp] theorem toFin_and (x y : BitVec v) :
+    BitVec.toFin (x &&& y) = BitVec.toFin x &&& BitVec.toFin y := by
+  apply Fin.eq_of_val_eq
+  exact (Nat.mod_eq_of_lt <| Nat.and_lt_two_pow _ y.isLt).symm
+
+@[simp] theorem getLsb_and {x y : BitVec v} : (x &&& y).getLsb i = (x.getLsb i && y.getLsb i) := by
+  rw [← testBit_toNat, getLsb, getLsb]
+  simp
+
+@[simp] theorem getMsb_and {x y : BitVec w} : (x &&& y).getMsb i = (x.getMsb i && y.getMsb i) := by
+  simp only [getMsb]
+  by_cases h : i < w <;> simp [h]
+
+@[simp] theorem msb_and {x y : BitVec w} : (x &&& y).msb = (x.msb && y.msb) := by
+  simp [BitVec.msb]
+
+@[simp] theorem truncate_and {x y : BitVec w} :
+    (x &&& y).truncate k = x.truncate k &&& y.truncate k := by
+  ext
+  simp
+
+/-! ### xor -/
+
+@[simp] theorem toNat_xor (x y : BitVec v) :
+    BitVec.toNat (x ^^^ y) = BitVec.toNat x ^^^ BitVec.toNat y := rfl
+
+@[simp] theorem toFin_xor (x y : BitVec v) :
+    BitVec.toFin (x ^^^ y) = BitVec.toFin x ^^^ BitVec.toFin y := by
+  apply Fin.eq_of_val_eq
+  exact (Nat.mod_eq_of_lt <| Nat.xor_lt_two_pow x.isLt y.isLt).symm
+
+@[simp] theorem getLsb_xor {x y : BitVec v} :
+    (x ^^^ y).getLsb i = (xor (x.getLsb i) (y.getLsb i)) := by
+  rw [← testBit_toNat, getLsb, getLsb]
+  simp
+
+@[simp] theorem truncate_xor {x y : BitVec w} :
+    (x ^^^ y).truncate k = x.truncate k ^^^ y.truncate k := by
+  ext
+  simp
+
+/-! ### not -/
+
+theorem not_def {x : BitVec v} : ~~~x = allOnes v ^^^ x := rfl
+
+@[simp, bv_toNat] theorem toNat_not {x : BitVec v} : (~~~x).toNat = 2^v - 1 - x.toNat := by
+  rw [Nat.sub_sub, Nat.add_comm, not_def, toNat_xor]
+  apply Nat.eq_of_testBit_eq
+  intro i
+  simp only [toNat_allOnes, Nat.testBit_xor, Nat.testBit_two_pow_sub_one]
+  match h : BitVec.toNat x with
+  | 0 => simp
+  | y+1 =>
+    rw [Nat.succ_eq_add_one] at h
+    rw [← h]
+    rw [Nat.testBit_two_pow_sub_succ (isLt _)]
+    · cases w : decide (i < v)
+      · simp at w
+        simp [w]
+        rw [Nat.testBit_lt_two_pow]
+        calc BitVec.toNat x < 2 ^ v := isLt _
+          _ ≤ 2 ^ i := Nat.pow_le_pow_of_le_right Nat.zero_lt_two w
+      · simp
+
+@[simp] theorem toFin_not (x : BitVec w) :
+    (~~~x).toFin = x.toFin.rev := by
+  apply Fin.val_inj.mp
+  simp only [val_toFin, toNat_not, Fin.val_rev]
+  omega
+
+@[simp] theorem getLsb_not {x : BitVec v} : (~~~x).getLsb i = (decide (i < v) && ! x.getLsb i) := by
+  by_cases h' : i < v <;> simp_all [not_def]
+
+@[simp] theorem truncate_not {x : BitVec w} (h : k ≤ w) :
+    (~~~x).truncate k = ~~~(x.truncate k) := by
+  ext
+  simp [h]
+  omega
+
+/-! ### cast -/
+
+@[simp] theorem not_cast {x : BitVec w} (h : w = w') : ~~~(cast h x) = cast h (~~~x) := by
+  ext
+  simp_all [lt_of_getLsb]
+
+@[simp] theorem and_cast {x y : BitVec w} (h : w = w') : cast h x &&& cast h y = cast h (x &&& y) := by
+  ext
+  simp_all [lt_of_getLsb]
+
+@[simp] theorem or_cast {x y : BitVec w} (h : w = w') : cast h x ||| cast h y = cast h (x ||| y) := by
+  ext
+  simp_all [lt_of_getLsb]
+
+@[simp] theorem xor_cast {x y : BitVec w} (h : w = w') : cast h x &&& cast h y = cast h (x &&& y) := by
+  ext
+  simp_all [lt_of_getLsb]
+
+/-! ### shiftLeft -/
+
+@[simp, bv_toNat] theorem toNat_shiftLeft {x : BitVec v} :
+    BitVec.toNat (x <<< n) = BitVec.toNat x <<< n % 2^v :=
+  BitVec.toNat_ofNat _ _
+
+@[simp] theorem toFin_shiftLeft {n : Nat} (x : BitVec w) :
+    BitVec.toFin (x <<< n) = Fin.ofNat' (x.toNat <<< n) (Nat.two_pow_pos w) := rfl
+
+@[simp] theorem getLsb_shiftLeft (x : BitVec m) (n) :
+    getLsb (x <<< n) i = (decide (i < m) && !decide (i < n) && getLsb x (i - n)) := by
+  rw [← testBit_toNat, getLsb]
+  simp only [toNat_shiftLeft, Nat.testBit_mod_two_pow, Nat.testBit_shiftLeft, ge_iff_le]
+  -- This step could be a case bashing tactic.
+  cases h₁ : decide (i < m) <;> cases h₂ : decide (n ≤ i) <;> cases h₃ : decide (i < n)
+  all_goals { simp_all <;> omega }
+
+@[simp] theorem getMsb_shiftLeft (x : BitVec w) (i) :
+    (x <<< i).getMsb k = x.getMsb (k + i) := by
+  simp only [getMsb, getLsb_shiftLeft]
+  by_cases h : w = 0
+  · subst h; simp
+  have t : w - 1 - k < w := by omega
+  simp only [t]
+  simp only [decide_True, Nat.sub_sub, Bool.true_and, Nat.add_assoc]
+  by_cases h₁ : k < w <;> by_cases h₂ : w - (1 + k) < i <;> by_cases h₃ : k + i < w
+    <;> simp [h₁, h₂, h₃]
+    <;> (first | apply getLsb_ge | apply Eq.symm; apply getLsb_ge)
+    <;> omega
+
+theorem shiftLeftZeroExtend_eq {x : BitVec w} :
+    shiftLeftZeroExtend x n = zeroExtend (w+n) x <<< n := by
+  apply eq_of_toNat_eq
+  rw [shiftLeftZeroExtend, zeroExtend]
+  split
+  · simp
+    rw [Nat.mod_eq_of_lt]
+    rw [Nat.shiftLeft_eq, Nat.pow_add]
+    exact Nat.mul_lt_mul_of_pos_right x.isLt (Nat.two_pow_pos _)
+  · omega
+
+@[simp] theorem getLsb_shiftLeftZeroExtend (x : BitVec m) (n : Nat) :
+    getLsb (shiftLeftZeroExtend x n) i = ((! decide (i < n)) && getLsb x (i - n)) := by
+  rw [shiftLeftZeroExtend_eq]
+  simp only [getLsb_shiftLeft, getLsb_zeroExtend]
+  cases h₁ : decide (i < n) <;> cases h₂ : decide (i - n < m + n) <;> cases h₃ : decide (i < m + n)
+    <;> simp_all
+    <;> (rw [getLsb_ge]; omega)
+
+@[simp] theorem getMsb_shiftLeftZeroExtend (x : BitVec m) (n : Nat) :
+    getMsb (shiftLeftZeroExtend x n) i = getMsb x i := by
+  have : n ≤ i + n := by omega
+  simp_all [shiftLeftZeroExtend_eq]
+
+@[simp] theorem msb_shiftLeftZeroExtend (x : BitVec w) (i : Nat) :
+    (shiftLeftZeroExtend x i).msb = x.msb := by
+  simp [shiftLeftZeroExtend_eq, BitVec.msb]
+
+/-! ### ushiftRight -/
+
+@[simp, bv_toNat] theorem toNat_ushiftRight (x : BitVec n) (i : Nat) :
+    (x >>> i).toNat = x.toNat >>> i := rfl
+
+@[simp] theorem getLsb_ushiftRight (x : BitVec n) (i j : Nat) :
+    getLsb (x >>> i) j = getLsb x (i+j) := by
+  unfold getLsb ; simp
+
+/-! ### append -/
+
+theorem append_def (x : BitVec v) (y : BitVec w) :
+    x ++ y = (shiftLeftZeroExtend x w ||| zeroExtend' (Nat.le_add_left w v) y) := rfl
+
+@[simp] theorem toNat_append (x : BitVec m) (y : BitVec n) :
+    (x ++ y).toNat = x.toNat <<< n ||| y.toNat :=
+  rfl
+
+@[simp] theorem getLsb_append {v : BitVec n} {w : BitVec m} :
+    getLsb (v ++ w) i = bif i < m then getLsb w i else getLsb v (i - m) := by
+  simp only [append_def, getLsb_or, getLsb_shiftLeftZeroExtend, getLsb_zeroExtend']
+  by_cases h : i < m
+  · simp [h]
+  · simp [h]; simp_all
+
+@[simp] theorem getMsb_append {v : BitVec n} {w : BitVec m} :
+    getMsb (v ++ w) i = bif n ≤ i then getMsb w (i - n) else getMsb v i := by
+  simp [append_def]
+  by_cases h : n ≤ i
+  · simp [h]
+  · simp [h]
+
+theorem msb_append {x : BitVec w} {y : BitVec v} :
+    (x ++ y).msb = bif (w == 0) then (y.msb) else (x.msb) := by
+  rw [← append_eq, append]
+  simp [msb_zeroExtend']
+  by_cases h : w = 0
+  · subst h
+    simp [BitVec.msb, getMsb]
+  · rw [cond_eq_if]
+    have q : 0 < w + v := by omega
+    have t : y.getLsb (w + v - 1) = false := getLsb_ge _ _ (by omega)
+    simp [h, q, t, BitVec.msb, getMsb]
+
+@[simp] theorem truncate_append {x : BitVec w} {y : BitVec v} :
+    (x ++ y).truncate k = if h : k ≤ v then y.truncate k else (x.truncate (k - v) ++ y).cast (by omega) := by
+  apply eq_of_getLsb_eq
+  intro i
+  simp only [getLsb_zeroExtend, Fin.is_lt, decide_True, getLsb_append, Bool.true_and]
+  split
+  · have t : i < v := by omega
+    simp [t]
+  · by_cases t : i < v
+    · simp [t]
+    · have t' : i - v < k - v := by omega
+      simp [t, t']
+
+@[simp] theorem truncate_cons {x : BitVec w} : (cons a x).truncate w = x := by
+  simp [cons]
+
+@[simp] theorem not_append {x : BitVec w} {y : BitVec v} : ~~~ (x ++ y) = (~~~ x) ++ (~~~ y) := by
+  ext i
+  simp only [getLsb_not, getLsb_append, cond_eq_if]
+  split
+  · simp_all
+  · simp_all; omega
+
+@[simp] theorem and_append {x₁ x₂ : BitVec w} {y₁ y₂ : BitVec v} :
+    (x₁ ++ y₁) &&& (x₂ ++ y₂) = (x₁ &&& x₂) ++ (y₁ &&& y₂) := by
+  ext i
+  simp only [getLsb_append, cond_eq_if]
+  split <;> simp [*]
+
+@[simp] theorem or_append {x₁ x₂ : BitVec w} {y₁ y₂ : BitVec v} :
+    (x₁ ++ y₁) ||| (x₂ ++ y₂) = (x₁ ||| x₂) ++ (y₁ ||| y₂) := by
+  ext i
+  simp only [getLsb_append, cond_eq_if]
+  split <;> simp [*]
+
+@[simp] theorem xor_append {x₁ x₂ : BitVec w} {y₁ y₂ : BitVec v} :
+    (x₁ ++ y₁) ^^^ (x₂ ++ y₂) = (x₁ ^^^ x₂) ++ (y₁ ^^^ y₂) := by
+  ext i
+  simp only [getLsb_append, cond_eq_if]
+  split <;> simp [*]
+
+/-! ### rev -/
+
+theorem getLsb_rev (x : BitVec w) (i : Fin w) :
+    x.getLsb i.rev = x.getMsb i := by
+  simp [getLsb, getMsb]
+  congr 1
+  omega
+
+theorem getMsb_rev (x : BitVec w) (i : Fin w) :
+    x.getMsb i.rev = x.getLsb i := by
+  simp only [← getLsb_rev]
+  simp only [Fin.rev]
+  congr
+  omega
+
+/-! ### cons -/
+
+@[simp] theorem toNat_cons (b : Bool) (x : BitVec w) :
+    (cons b x).toNat = (b.toNat <<< w) ||| x.toNat := by
+  let ⟨x, _⟩ := x
+  simp [cons, toNat_append, toNat_ofBool]
+
+/-- Variant of `toNat_cons` using `+` instead of `|||`. -/
+theorem toNat_cons' {x : BitVec w} :
+    (cons a x).toNat = (a.toNat <<< w) + x.toNat := by
+  simp [cons, Nat.shiftLeft_eq, Nat.mul_comm _ (2^w), Nat.mul_add_lt_is_or, x.isLt]
+
+@[simp] theorem getLsb_cons (b : Bool) {n} (x : BitVec n) (i : Nat) :
+    getLsb (cons b x) i = if i = n then b else getLsb x i := by
+  simp only [getLsb, toNat_cons, Nat.testBit_or]
+  rw [Nat.testBit_shiftLeft]
+  rcases Nat.lt_trichotomy i n with i_lt_n | i_eq_n | n_lt_i
+  · have p1 : ¬(n ≤ i) := by omega
+    have p2 : i ≠ n := by omega
+    simp [p1, p2]
+  · simp [i_eq_n, testBit_toNat]
+    cases b <;> trivial
+  · have p1 : i ≠ n := by omega
+    have p2 : i - n ≠ 0 := by omega
+    simp [p1, p2, Nat.testBit_bool_to_nat]
+
+@[simp] theorem msb_cons : (cons a x).msb = a := by
+  simp [cons, msb_cast, msb_append]
+
+@[simp] theorem getMsb_cons_zero : (cons a x).getMsb 0 = a := by
+  rw [← BitVec.msb, msb_cons]
+
+@[simp] theorem getMsb_cons_succ : (cons a x).getMsb (i + 1) = x.getMsb i := by
+  simp [cons, cond_eq_if]
+  omega
+
+theorem truncate_succ (x : BitVec w) :
+    truncate (i+1) x = cons (getLsb x i) (truncate i x) := by
+  apply eq_of_getLsb_eq
+  intro j
+  simp only [getLsb_truncate, getLsb_cons, j.isLt, decide_True, Bool.true_and]
+  if j_eq : j.val = i then
+    simp [j_eq]
+  else
+    have j_lt : j.val < i := Nat.lt_of_le_of_ne (Nat.le_of_succ_le_succ j.isLt) j_eq
+    simp [j_eq, j_lt]
+
+theorem eq_msb_cons_truncate (x : BitVec (w+1)) : x = (cons x.msb (x.truncate w)) := by
+  ext i
+  simp
+  split <;> rename_i h
+  · simp [BitVec.msb, getMsb, h]
+  · by_cases h' : i < w
+    · simp_all
+    · omega
+
+@[simp] theorem not_cons (x : BitVec w) (b : Bool) : ~~~(cons b x) = cons (!b) (~~~x) := by
+  simp [cons]
+
+@[simp] theorem cons_or_cons (x y : BitVec w) (a b : Bool) :
+    (cons a x) ||| (cons b y) = cons (a || b) (x ||| y) := by
+  ext i; cases i using Fin.succRecOn <;> simp <;> split <;> rfl
+
+@[simp] theorem cons_and_cons (x y : BitVec w) (a b : Bool) :
+    (cons a x) &&& (cons b y) = cons (a && b) (x &&& y) := by
+  ext i; cases i using Fin.succRecOn <;> simp <;> split <;> rfl
+
+@[simp] theorem cons_xor_cons (x y : BitVec w) (a b : Bool) :
+    (cons a x) ^^^ (cons b y) = cons (xor a b) (x ^^^ y) := by
+  ext i; cases i using Fin.succRecOn <;> simp <;> split <;> rfl
+
+/-! ### concat -/
+
+@[simp] theorem toNat_concat (x : BitVec w) (b : Bool) :
+    (concat x b).toNat = x.toNat * 2 + b.toNat := by
+  apply Nat.eq_of_testBit_eq
+  simp only [concat, toNat_append, Nat.shiftLeft_eq, Nat.pow_one, toNat_ofBool, Nat.testBit_or]
+  cases b
+  · simp
+  · rintro (_ | i)
+    <;> simp [Nat.add_mod, Nat.add_comm, Nat.add_mul_div_right]
+
+theorem getLsb_concat (x : BitVec w) (b : Bool) (i : Nat) :
+    (concat x b).getLsb i = if i = 0 then b else x.getLsb (i - 1) := by
+  simp only [concat, getLsb, toNat_append, toNat_ofBool, Nat.testBit_or, Nat.shiftLeft_eq]
+  cases i
+  · simp [Nat.mod_eq_of_lt b.toNat_lt]
+  · simp [Nat.div_eq_of_lt b.toNat_lt]
+
+@[simp] theorem getLsb_concat_zero : (concat x b).getLsb 0 = b := by
+  simp [getLsb_concat]
+
+@[simp] theorem getLsb_concat_succ : (concat x b).getLsb (i + 1) = x.getLsb i := by
+  simp [getLsb_concat]
+
+@[simp] theorem not_concat (x : BitVec w) (b : Bool) : ~~~(concat x b) = concat (~~~x) !b := by
+  ext i; cases i using Fin.succRecOn <;> simp [*, Nat.succ_lt_succ]
+
+@[simp] theorem concat_or_concat (x y : BitVec w) (a b : Bool) :
+    (concat x a) ||| (concat y b) = concat (x ||| y) (a || b) := by
+  ext i; cases i using Fin.succRecOn <;> simp
+
+@[simp] theorem concat_and_concat (x y : BitVec w) (a b : Bool) :
+    (concat x a) &&& (concat y b) = concat (x &&& y) (a && b) := by
+  ext i; cases i using Fin.succRecOn <;> simp
+
+@[simp] theorem concat_xor_concat (x y : BitVec w) (a b : Bool) :
+    (concat x a) ^^^ (concat y b) = concat (x ^^^ y) (xor a b) := by
+  ext i; cases i using Fin.succRecOn <;> simp
+
+/-! ### add -/
+
+theorem add_def {n} (x y : BitVec n) : x + y = .ofNat n (x.toNat + y.toNat) := rfl
+
+/--
+Definition of bitvector addition as a nat.
+-/
+@[simp, bv_toNat] theorem toNat_add (x y : BitVec w) : (x + y).toNat = (x.toNat + y.toNat) % 2^w := rfl
+@[simp] theorem toFin_add (x y : BitVec w) : (x + y).toFin = toFin x + toFin y := rfl
+@[simp] theorem ofFin_add (x : Fin (2^n)) (y : BitVec n) :
+  .ofFin x + y = .ofFin (x + y.toFin) := rfl
+@[simp] theorem add_ofFin (x : BitVec n) (y : Fin (2^n)) :
+  x + .ofFin y = .ofFin (x.toFin + y) := rfl
+@[simp] theorem ofNat_add_ofNat {n} (x y : Nat) : x#n + y#n = (x + y)#n := by
+  apply eq_of_toNat_eq ; simp [BitVec.ofNat]
+
+protected theorem add_assoc (x y z : BitVec n) : x + y + z = x + (y + z) := by
+  apply eq_of_toNat_eq ; simp [Nat.add_assoc]
+
+protected theorem add_comm (x y : BitVec n) : x + y = y + x := by
+  simp [add_def, Nat.add_comm]
+
+@[simp] protected theorem add_zero (x : BitVec n) : x + 0#n = x := by simp [add_def]
+
+@[simp] protected theorem zero_add (x : BitVec n) : 0#n + x = x := by simp [add_def]
+
+theorem truncate_add (x y : BitVec w) (h : i ≤ w) :
+    (x + y).truncate i = x.truncate i + y.truncate i := by
+  have dvd : 2^i ∣ 2^w := Nat.pow_dvd_pow _ h
+  simp [bv_toNat, h, Nat.mod_mod_of_dvd _ dvd]
+
+/-! ### sub/neg -/
+
+theorem sub_def {n} (x y : BitVec n) : x - y = .ofNat n (x.toNat + (2^n - y.toNat)) := by rfl
+
+@[simp, bv_toNat] theorem toNat_sub {n} (x y : BitVec n) :
+  (x - y).toNat = ((x.toNat + (2^n - y.toNat)) % 2^n) := rfl
+@[simp] theorem toFin_sub (x y : BitVec n) : (x - y).toFin = toFin x - toFin y := rfl
+
+@[simp] theorem ofFin_sub (x : Fin (2^n)) (y : BitVec n) : .ofFin x - y = .ofFin (x - y.toFin) :=
+  rfl
+@[simp] theorem sub_ofFin (x : BitVec n) (y : Fin (2^n)) : x - .ofFin y = .ofFin (x.toFin - y) :=
+  rfl
+-- Remark: we don't use `[simp]` here because simproc` subsumes it for literals.
+-- If `x` and `n` are not literals, applying this theorem eagerly may not be a good idea.
+theorem ofNat_sub_ofNat {n} (x y : Nat) : x#n - y#n = .ofNat n (x + (2^n - y % 2^n)) := by
+  apply eq_of_toNat_eq ; simp [BitVec.ofNat]
+
+@[simp] protected theorem sub_zero (x : BitVec n) : x - (0#n) = x := by apply eq_of_toNat_eq ; simp
+
+@[simp] protected theorem sub_self (x : BitVec n) : x - x = 0#n := by
+  apply eq_of_toNat_eq
+  simp only [toNat_sub]
+  rw [Nat.add_sub_of_le]
+  · simp
+  · exact Nat.le_of_lt x.isLt
+
+@[simp, bv_toNat] theorem toNat_neg (x : BitVec n) : (- x).toNat = (2^n - x.toNat) % 2^n := by
+  simp [Neg.neg, BitVec.neg]
+
+theorem sub_toAdd {n} (x y : BitVec n) : x - y = x + - y := by
+  apply eq_of_toNat_eq
+  simp
+
+@[simp] theorem neg_zero (n:Nat) : -0#n = 0#n := by apply eq_of_toNat_eq ; simp
+
+theorem add_sub_cancel (x y : BitVec w) : x + y - y = x := by
+  apply eq_of_toNat_eq
+  have y_toNat_le := Nat.le_of_lt y.toNat_lt
+  rw [toNat_sub, toNat_add, Nat.mod_add_mod, Nat.add_assoc, ← Nat.add_sub_assoc y_toNat_le,
+    Nat.add_sub_cancel_left, Nat.add_mod_right, toNat_mod_cancel]
+
+theorem negOne_eq_allOnes : -1#w = allOnes w := by
+  apply eq_of_toNat_eq
+  if g : w = 0 then
+    simp [g]
+  else
+    have q : 1 < 2^w := by simp [g]
+    have r : (2^w - 1) < 2^w := by omega
+    simp [Nat.mod_eq_of_lt q, Nat.mod_eq_of_lt r]
+
+/-! ### mul -/
+
+theorem mul_def {n} {x y : BitVec n} : x * y = (ofFin <| x.toFin * y.toFin) := by rfl
+
+@[simp, bv_toNat] theorem toNat_mul (x y : BitVec n) : (x * y).toNat = (x.toNat * y.toNat) % 2 ^ n := rfl
+@[simp] theorem toFin_mul (x y : BitVec n) : (x * y).toFin = (x.toFin * y.toFin) := rfl
+
+protected theorem mul_comm (x y : BitVec w) : x * y = y * x := by
+  apply eq_of_toFin_eq; simpa using Fin.mul_comm ..
+instance : Std.Commutative (fun (x y : BitVec w) => x * y) := ⟨BitVec.mul_comm⟩
+
+protected theorem mul_assoc (x y z : BitVec w) : x * y * z = x * (y * z) := by
+  apply eq_of_toFin_eq; simpa using Fin.mul_assoc ..
+instance : Std.Associative (fun (x y : BitVec w) => x * y) := ⟨BitVec.mul_assoc⟩
+
+@[simp] protected theorem mul_one (x : BitVec w) : x * 1#w = x := by
+  cases w
+  · apply Subsingleton.elim
+  · apply eq_of_toNat_eq; simp [Nat.mod_eq_of_lt]
+
+@[simp] protected theorem one_mul (x : BitVec w) : 1#w * x = x := by
+  rw [BitVec.mul_comm, BitVec.mul_one]
+
+instance : Std.LawfulCommIdentity (fun (x y : BitVec w) => x * y) (1#w) where
+  right_id := BitVec.mul_one
+
+/-! ### le and lt -/
+
+@[bv_toNat] theorem le_def (x y : BitVec n) :
+  x ≤ y ↔ x.toNat ≤ y.toNat := Iff.rfl
+
+@[simp] theorem le_ofFin (x : BitVec n) (y : Fin (2^n)) :
+  x ≤ BitVec.ofFin y ↔ x.toFin ≤ y := Iff.rfl
+@[simp] theorem ofFin_le (x : Fin (2^n)) (y : BitVec n) :
+  BitVec.ofFin x ≤ y ↔ x ≤ y.toFin := Iff.rfl
+@[simp] theorem ofNat_le_ofNat {n} (x y : Nat) : (x#n) ≤ (y#n) ↔ x % 2^n ≤ y % 2^n := by
+  simp [le_def]
+
+@[bv_toNat] theorem lt_def (x y : BitVec n) :
+  x < y ↔ x.toNat < y.toNat := Iff.rfl
+
+@[simp] theorem lt_ofFin (x : BitVec n) (y : Fin (2^n)) :
+  x < BitVec.ofFin y ↔ x.toFin < y := Iff.rfl
+@[simp] theorem ofFin_lt (x : Fin (2^n)) (y : BitVec n) :
+  BitVec.ofFin x < y ↔ x < y.toFin := Iff.rfl
+@[simp] theorem ofNat_lt_ofNat {n} (x y : Nat) : (x#n) < (y#n) ↔ x % 2^n < y % 2^n := by
+  simp [lt_def]
+
+protected theorem lt_of_le_ne (x y : BitVec n) (h1 : x <= y) (h2 : ¬ x = y) : x < y := by
+  revert h1 h2
+  let ⟨x, lt⟩ := x
+  let ⟨y, lt⟩ := y
+  simp
+  exact Nat.lt_of_le_of_ne
+
+/-! ### intMax -/
+
+/-- The bitvector of width `w` that has the largest value when interpreted as an integer. -/
+def intMax (w : Nat) : BitVec w  := (2^w - 1)#w
+
+theorem getLsb_intMax_eq (w : Nat) : (intMax w).getLsb i = decide (i < w) := by
+  simp [intMax, getLsb]
+
+theorem toNat_intMax_eq : (intMax w).toNat = 2^w - 1 := by
+  have h : 2^w - 1 < 2^w := by
+    have pos : 2^w > 0 := Nat.pow_pos (by decide)
+    omega
+  simp [intMax, Nat.shiftLeft_eq, Nat.one_mul, natCast_eq_ofNat, toNat_ofNat, Nat.mod_eq_of_lt h]
+
+/-! ### ofBoolList -/
+
+@[simp] theorem getMsb_ofBoolListBE : (ofBoolListBE bs).getMsb i = bs.getD i false := by
+  induction bs generalizing i <;> cases i <;> simp_all [ofBoolListBE]
+
+@[simp] theorem getLsb_ofBoolListBE :
+    (ofBoolListBE bs).getLsb i = (decide (i < bs.length) && bs.getD (bs.length - 1 - i) false) := by
+  simp [getLsb_eq_getMsb]
+
+@[simp] theorem getLsb_ofBoolListLE : (ofBoolListLE bs).getLsb i = bs.getD i false := by
+  induction bs generalizing i <;> cases i <;> simp_all [ofBoolListLE]
+
+@[simp] theorem getMsb_ofBoolListLE :
+    (ofBoolListLE bs).getMsb i = (decide (i < bs.length) && bs.getD (bs.length - 1 - i) false) := by
+  simp [getMsb_eq_getLsb]
+
+end BitVec

src/Init/Data/Bool.lean

@@ -0,0 +1,502 @@
+/-
+Copyright (c) 2023 F. G. Dorais. No rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: F. G. Dorais
+-/
+prelude
+import Init.BinderPredicates
+
+/-- Boolean exclusive or -/
+abbrev xor : Bool → Bool → Bool := bne
+
+namespace Bool
+
+/- Namespaced versions that can be used instead of prefixing `_root_` -/
+@[inherit_doc not] protected abbrev not := not
+@[inherit_doc or]  protected abbrev or  := or
+@[inherit_doc and] protected abbrev and := and
+@[inherit_doc xor] protected abbrev xor := xor
+
+instance (p : Bool → Prop) [inst : DecidablePred p] : Decidable (∀ x, p x) :=
+  match inst true, inst false with
+  | isFalse ht, _ => isFalse fun h => absurd (h _) ht
+  | _, isFalse hf => isFalse fun h => absurd (h _) hf
+  | isTrue ht, isTrue hf => isTrue fun | true => ht | false => hf
+
+instance (p : Bool → Prop) [inst : DecidablePred p] : Decidable (∃ x, p x) :=
+  match inst true, inst false with
+  | isTrue ht, _ => isTrue ⟨_, ht⟩
+  | _, isTrue hf => isTrue ⟨_, hf⟩
+  | isFalse ht, isFalse hf => isFalse fun | ⟨true, h⟩ => absurd h ht | ⟨false, h⟩ => absurd h hf
+
+@[simp] theorem default_bool : default = false := rfl
+
+instance : LE Bool := ⟨(. → .)⟩
+instance : LT Bool := ⟨(!. && .)⟩
+
+instance (x y : Bool) : Decidable (x ≤ y) := inferInstanceAs (Decidable (x → y))
+instance (x y : Bool) : Decidable (x < y) := inferInstanceAs (Decidable (!x && y))
+
+instance : Max Bool := ⟨or⟩
+instance : Min Bool := ⟨and⟩
+
+theorem false_ne_true : false ≠ true := Bool.noConfusion
+
+theorem eq_false_or_eq_true : (b : Bool) → b = true ∨ b = false := by decide
+
+theorem eq_false_iff : {b : Bool} → b = false ↔ b ≠ true := by decide
+
+theorem ne_false_iff : {b : Bool} → b ≠ false ↔ b = true := by decide
+
+theorem eq_iff_iff {a b : Bool} : a = b ↔ (a ↔ b) := by cases b <;> simp
+
+@[simp] theorem decide_eq_true  {b : Bool} [Decidable (b = true)]  : decide (b = true)  =  b := by cases b <;> simp
+@[simp] theorem decide_eq_false {b : Bool} [Decidable (b = false)] : decide (b = false) = !b := by cases b <;> simp
+@[simp] theorem decide_true_eq  {b : Bool} [Decidable (true = b)]  : decide (true  = b) =  b := by cases b <;> simp
+@[simp] theorem decide_false_eq {b : Bool} [Decidable (false = b)] : decide (false = b) = !b := by cases b <;> simp
+
+/-! ### and -/
+
+@[simp] theorem and_self_left  : ∀(a b : Bool), (a && (a && b)) = (a && b) := by decide
+@[simp] theorem and_self_right : ∀(a b : Bool), ((a && b) && b) = (a && b) := by decide
+
+@[simp] theorem not_and_self : ∀ (x : Bool), (!x && x) = false := by decide
+@[simp] theorem and_not_self : ∀ (x : Bool), (x && !x) = false := by decide
+
+/-
+Added for confluence with `not_and_self` `and_not_self` on term
+`(b && !b) = true` due to reductions:
+
+1. `(b = true ∨ !b = true)` via `Bool.and_eq_true`
+2. `false = true` via `Bool.and_not_self`
+-/
+@[simp] theorem eq_true_and_eq_false_self : ∀(b : Bool), (b = true ∧ b = false) ↔ False := by decide
+@[simp] theorem eq_false_and_eq_true_self : ∀(b : Bool), (b = false ∧ b = true) ↔ False := by decide
+
+theorem and_comm : ∀ (x y : Bool), (x && y) = (y && x) := by decide
+
+theorem and_left_comm : ∀ (x y z : Bool), (x && (y && z)) = (y && (x && z)) := by decide
+theorem and_right_comm : ∀ (x y z : Bool), ((x && y) && z) = ((x && z) && y) := by decide
+
+/-
+Bool version `and_iff_left_iff_imp`.
+
+Needed for confluence of term `(a && b) ↔ a` which reduces to `(a && b) = a` via
+`Bool.coe_iff_coe` and `a → b` via `Bool.and_eq_true` and
+`and_iff_left_iff_imp`.
+-/
+@[simp] theorem and_iff_left_iff_imp  : ∀(a b : Bool), ((a && b) = a) ↔ (a → b) := by decide
+@[simp] theorem and_iff_right_iff_imp : ∀(a b : Bool), ((a && b) = b) ↔ (b → a) := by decide
+@[simp] theorem iff_self_and : ∀(a b : Bool), (a = (a && b)) ↔ (a → b) := by decide
+@[simp] theorem iff_and_self : ∀(a b : Bool), (b = (a && b)) ↔ (b → a) := by decide
+
+/-! ### or -/
+
+@[simp] theorem or_self_left  : ∀(a b : Bool), (a || (a || b)) = (a || b) := by decide
+@[simp] theorem or_self_right : ∀(a b : Bool), ((a || b) || b) = (a || b) := by decide
+
+@[simp] theorem not_or_self : ∀ (x : Bool), (!x || x) = true := by decide
+@[simp] theorem or_not_self : ∀ (x : Bool), (x || !x) = true := by decide
+
+/-
+Added for confluence with `not_or_self` `or_not_self` on term
+`(b || !b) = true` due to reductions:
+1. `(b = true ∨ !b = true)` via `Bool.or_eq_true`
+2. `true = true` via `Bool.or_not_self`
+-/
+@[simp] theorem eq_true_or_eq_false_self : ∀(b : Bool), (b = true ∨ b = false) ↔ True := by decide
+@[simp] theorem eq_false_or_eq_true_self : ∀(b : Bool), (b = false ∨ b = true) ↔ True := by decide
+
+/-
+Bool version `or_iff_left_iff_imp`.
+
+Needed for confluence of term `(a || b) ↔ a` which reduces to `(a || b) = a` via
+`Bool.coe_iff_coe` and `a → b` via `Bool.or_eq_true` and
+`and_iff_left_iff_imp`.
+-/
+@[simp] theorem or_iff_left_iff_imp  : ∀(a b : Bool), ((a || b) = a) ↔ (b → a) := by decide
+@[simp] theorem or_iff_right_iff_imp : ∀(a b : Bool), ((a || b) = b) ↔ (a → b) := by decide
+@[simp] theorem iff_self_or : ∀(a b : Bool), (a = (a || b)) ↔ (b → a) := by decide
+@[simp] theorem iff_or_self : ∀(a b : Bool), (b = (a || b)) ↔ (a → b) := by decide
+
+theorem or_comm : ∀ (x y : Bool), (x || y) = (y || x) := by decide
+
+theorem or_left_comm : ∀ (x y z : Bool), (x || (y || z)) = (y || (x || z)) := by decide
+theorem or_right_comm : ∀ (x y z : Bool), ((x || y) || z) = ((x || z) || y) := by decide
+
+/-! ### distributivity -/
+
+theorem and_or_distrib_left  : ∀ (x y z : Bool), (x && (y || z)) = (x && y || x && z) := by decide
+theorem and_or_distrib_right : ∀ (x y z : Bool), ((x || y) && z) = (x && z || y && z) := by decide
+
+theorem or_and_distrib_left  : ∀ (x y z : Bool), (x || y && z) = ((x || y) && (x || z)) := by decide
+theorem or_and_distrib_right : ∀ (x y z : Bool), (x && y || z) = ((x || z) && (y || z)) := by decide
+
+theorem and_xor_distrib_left : ∀ (x y z : Bool), (x && xor y z) = xor (x && y) (x && z) := by decide
+theorem and_xor_distrib_right : ∀ (x y z : Bool), (xor x y && z) = xor (x && z) (y && z) := by decide
+
+/-- De Morgan's law for boolean and -/
+@[simp] theorem not_and : ∀ (x y : Bool), (!(x && y)) = (!x || !y) := by decide
+
+/-- De Morgan's law for boolean or -/
+@[simp] theorem not_or : ∀ (x y : Bool), (!(x || y)) = (!x && !y) := by decide
+
+theorem and_eq_true_iff (x y : Bool) : (x && y) = true ↔ x = true ∧ y = true :=
+  Iff.of_eq (and_eq_true x y)
+
+theorem and_eq_false_iff : ∀ (x y : Bool), (x && y) = false ↔ x = false ∨ y = false := by decide
+
+/-
+New simp rule that replaces `Bool.and_eq_false_eq_eq_false_or_eq_false` in
+Mathlib due to confluence:
+
+Consider the term: `¬((b && c) = true)`:
+
+1. Reduces to `((b && c) = false)` via `Bool.not_eq_true`
+2. Reduces to `¬(b = true ∧ c = true)` via `Bool.and_eq_true`.
+
+
+1. Further reduces to `b = false ∨ c = false` via `Bool.and_eq_false_eq_eq_false_or_eq_false`.
+2. Further reduces to `b = true → c = false` via `not_and` and `Bool.not_eq_true`.
+-/
+@[simp] theorem and_eq_false_imp : ∀ (x y : Bool), (x && y) = false ↔ (x = true → y = false) := by decide
+
+@[simp] theorem or_eq_true_iff : ∀ (x y : Bool), (x || y) = true ↔ x = true ∨ y = true := by decide
+
+@[simp] theorem or_eq_false_iff : ∀ (x y : Bool), (x || y) = false ↔ x = false ∧ y = false := by decide
+
+/-! ### eq/beq/bne -/
+
+/--
+These two rules follow trivially by simp, but are needed to avoid non-termination
+in false_eq and true_eq.
+-/
+@[simp] theorem false_eq_true : (false = true) = False := by simp
+@[simp] theorem true_eq_false : (true = false) = False := by simp
+
+-- The two lemmas below normalize terms with a constant to the
+-- right-hand side but risk non-termination if `false_eq_true` and
+-- `true_eq_false` are disabled.
+@[simp low] theorem false_eq (b : Bool) : (false = b) = (b = false) := by
+  cases b <;> simp
+
+@[simp low] theorem true_eq (b : Bool) : (true = b) = (b = true) := by
+  cases b <;> simp
+
+@[simp] theorem true_beq  : ∀b, (true  == b) =  b := by decide
+@[simp] theorem false_beq : ∀b, (false == b) = !b := by decide
+@[simp] theorem beq_true  : ∀b, (b == true)  =  b := by decide
+@[simp] theorem beq_false : ∀b, (b == false) = !b := by decide
+
+@[simp] theorem true_bne  : ∀(b : Bool), (true  != b) = !b := by decide
+@[simp] theorem false_bne : ∀(b : Bool), (false != b) =  b := by decide
+@[simp] theorem bne_true  : ∀(b : Bool), (b != true)  = !b := by decide
+@[simp] theorem bne_false : ∀(b : Bool), (b != false) =  b := by decide
+
+@[simp] theorem not_beq_self : ∀ (x : Bool), ((!x) == x) = false := by decide
+@[simp] theorem beq_not_self : ∀ (x : Bool), (x   == !x) = false := by decide
+
+@[simp] theorem not_bne_self : ∀ (x : Bool), ((!x) != x) = true := by decide
+@[simp] theorem bne_not_self : ∀ (x : Bool), (x   != !x) = true := by decide
+
+/-
+Added for equivalence with `Bool.not_beq_self` and needed for confluence
+due to `beq_iff_eq`.
+-/
+@[simp] theorem not_eq_self : ∀(b : Bool), ((!b) = b) ↔ False := by decide
+@[simp] theorem eq_not_self : ∀(b : Bool), (b = (!b)) ↔ False := by decide
+
+@[simp] theorem beq_self_left  : ∀(a b : Bool), (a == (a == b)) = b := by decide
+@[simp] theorem beq_self_right : ∀(a b : Bool), ((a == b) == b) = a := by decide
+@[simp] theorem bne_self_left  : ∀(a b : Bool), (a != (a != b)) = b := by decide
+@[simp] theorem bne_self_right : ∀(a b : Bool), ((a != b) != b) = a := by decide
+
+@[simp] theorem not_bne_not : ∀ (x y : Bool), ((!x) != (!y)) = (x != y) := by decide
+
+@[simp] theorem bne_assoc : ∀ (x y z : Bool), ((x != y) != z) = (x != (y != z)) := by decide
+
+@[simp] theorem bne_left_inj  : ∀ (x y z : Bool), (x != y) = (x != z) ↔ y = z := by decide
+@[simp] theorem bne_right_inj : ∀ (x y z : Bool), (x != z) = (y != z) ↔ x = y := by decide
+
+/-! ### coercision related normal forms -/
+
+@[simp] theorem not_eq_not : ∀ {a b : Bool}, ¬a = !b ↔ a = b := by decide
+
+@[simp] theorem not_not_eq : ∀ {a b : Bool}, ¬(!a) = b ↔ a = b := by decide
+
+@[simp] theorem coe_iff_coe : ∀(a b : Bool), (a ↔ b) ↔ a = b := by decide
+
+@[simp] theorem coe_true_iff_false  : ∀(a b : Bool), (a ↔ b = false) ↔ a = (!b) := by decide
+@[simp] theorem coe_false_iff_true  : ∀(a b : Bool), (a = false ↔ b) ↔ (!a) = b := by decide
+@[simp] theorem coe_false_iff_false : ∀(a b : Bool), (a = false ↔ b = false) ↔ (!a) = (!b) := by decide
+
+/-! ### xor -/
+
+theorem false_xor : ∀ (x : Bool), xor false x = x := false_bne
+
+theorem xor_false : ∀ (x : Bool), xor x false = x := bne_false
+
+theorem true_xor : ∀ (x : Bool), xor true x = !x := true_bne
+
+theorem xor_true : ∀ (x : Bool), xor x true = !x := bne_true
+
+theorem not_xor_self : ∀ (x : Bool), xor (!x) x = true := not_bne_self
+
+theorem xor_not_self : ∀ (x : Bool), xor x (!x) = true := bne_not_self
+
+theorem not_xor : ∀ (x y : Bool), xor (!x) y = !(xor x y) := by decide
+
+theorem xor_not : ∀ (x y : Bool), xor x (!y) = !(xor x y) := by decide
+
+theorem not_xor_not : ∀ (x y : Bool), xor (!x) (!y) = (xor x y) := not_bne_not
+
+theorem xor_self : ∀ (x : Bool), xor x x = false := by decide
+
+theorem xor_comm : ∀ (x y : Bool), xor x y = xor y x := by decide
+
+theorem xor_left_comm : ∀ (x y z : Bool), xor x (xor y z) = xor y (xor x z) := by decide
+
+theorem xor_right_comm : ∀ (x y z : Bool), xor (xor x y) z = xor (xor x z) y := by decide
+
+theorem xor_assoc : ∀ (x y z : Bool), xor (xor x y) z = xor x (xor y z) := bne_assoc
+
+theorem xor_left_inj : ∀ (x y z : Bool), xor x y = xor x z ↔ y = z := bne_left_inj
+
+theorem xor_right_inj : ∀ (x y z : Bool), xor x z = xor y z ↔ x = y := bne_right_inj
+
+/-! ### le/lt -/
+
+@[simp] protected theorem le_true : ∀ (x : Bool), x ≤ true := by decide
+
+@[simp] protected theorem false_le : ∀ (x : Bool), false ≤ x := by decide
+
+@[simp] protected theorem le_refl : ∀ (x : Bool), x ≤ x := by decide
+
+@[simp] protected theorem lt_irrefl : ∀ (x : Bool), ¬ x < x := by decide
+
+protected theorem le_trans : ∀ {x y z : Bool}, x ≤ y → y ≤ z → x ≤ z := by decide
+
+protected theorem le_antisymm : ∀ {x y : Bool}, x ≤ y → y ≤ x → x = y := by decide
+
+protected theorem le_total : ∀ (x y : Bool), x ≤ y ∨ y ≤ x := by decide
+
+protected theorem lt_asymm : ∀ {x y : Bool}, x < y → ¬ y < x := by decide
+
+protected theorem lt_trans : ∀ {x y z : Bool}, x < y → y < z → x < z := by decide
+
+protected theorem lt_iff_le_not_le : ∀ {x y : Bool}, x < y ↔ x ≤ y ∧ ¬ y ≤ x := by decide
+
+protected theorem lt_of_le_of_lt : ∀ {x y z : Bool}, x ≤ y → y < z → x < z := by decide
+
+protected theorem lt_of_lt_of_le : ∀ {x y z : Bool}, x < y → y ≤ z → x < z := by decide
+
+protected theorem le_of_lt : ∀ {x y : Bool}, x < y → x ≤ y := by decide
+
+protected theorem le_of_eq : ∀ {x y : Bool}, x = y → x ≤ y := by decide
+
+protected theorem ne_of_lt : ∀ {x y : Bool}, x < y → x ≠ y := by decide
+
+protected theorem lt_of_le_of_ne : ∀ {x y : Bool}, x ≤ y → x ≠ y → x < y := by decide
+
+protected theorem le_of_lt_or_eq : ∀ {x y : Bool}, x < y ∨ x = y → x ≤ y := by decide
+
+protected theorem eq_true_of_true_le : ∀ {x : Bool}, true ≤ x → x = true := by decide
+
+protected theorem eq_false_of_le_false : ∀ {x : Bool}, x ≤ false → x = false := by decide
+
+/-! ### min/max -/
+
+@[simp] protected theorem max_eq_or : max = or := rfl
+
+@[simp] protected theorem min_eq_and : min = and := rfl
+
+/-! ### injectivity lemmas -/
+
+theorem not_inj : ∀ {x y : Bool}, (!x) = (!y) → x = y := by decide
+
+theorem not_inj_iff : ∀ {x y : Bool}, (!x) = (!y) ↔ x = y := by decide
+
+theorem and_or_inj_right : ∀ {m x y : Bool}, (x && m) = (y && m) → (x || m) = (y || m) → x = y := by
+  decide
+
+theorem and_or_inj_right_iff :
+    ∀ {m x y : Bool}, (x && m) = (y && m) ∧ (x || m) = (y || m) ↔ x = y := by decide
+
+theorem and_or_inj_left : ∀ {m x y : Bool}, (m && x) = (m && y) → (m || x) = (m || y) → x = y := by
+  decide
+
+theorem and_or_inj_left_iff :
+    ∀ {m x y : Bool}, (m && x) = (m && y) ∧ (m || x) = (m || y) ↔ x = y := by decide
+
+/-! ## toNat -/
+
+/-- convert a `Bool` to a `Nat`, `false -> 0`, `true -> 1` -/
+def toNat (b:Bool) : Nat := cond b 1 0
+
+@[simp] theorem toNat_false : false.toNat = 0 := rfl
+
+@[simp] theorem toNat_true : true.toNat = 1 := rfl
+
+theorem toNat_le (c : Bool) : c.toNat ≤ 1 := by
+  cases c <;> trivial
+
+@[deprecated toNat_le] abbrev toNat_le_one := toNat_le
+
+theorem toNat_lt (b : Bool) : b.toNat < 2 :=
+  Nat.lt_succ_of_le (toNat_le _)
+
+@[simp] theorem toNat_eq_zero (b : Bool) : b.toNat = 0 ↔ b = false := by
+  cases b <;> simp
+@[simp] theorem toNat_eq_one  (b : Bool) : b.toNat = 1 ↔ b = true := by
+  cases b <;> simp
+
+/-! ### ite -/
+
+@[simp] theorem if_true_left  (p : Prop) [h : Decidable p] (f : Bool) :
+    (ite p true f) = (p || f) := by cases h with | _ p => simp [p]
+
+@[simp] theorem if_false_left  (p : Prop) [h : Decidable p] (f : Bool) :
+    (ite p false f) = (!p && f) := by cases h with | _ p => simp [p]
+
+@[simp] theorem if_true_right  (p : Prop) [h : Decidable p] (t : Bool) :
+    (ite p t true) = (!(p : Bool) || t) := by cases h with | _ p => simp [p]
+
+@[simp] theorem if_false_right  (p : Prop) [h : Decidable p] (t : Bool) :
+    (ite p t false) = (p && t) := by cases h with | _ p => simp [p]
+
+@[simp] theorem ite_eq_true_distrib (p : Prop) [h : Decidable p] (t f : Bool) :
+    (ite p t f = true) = ite p (t = true) (f = true) := by
+  cases h with | _ p => simp [p]
+
+@[simp] theorem ite_eq_false_distrib (p : Prop) [h : Decidable p] (t f : Bool) :
+    (ite p t f = false) = ite p (t = false) (f = false) := by
+  cases h with | _ p => simp [p]
+
+/-
+`not_ite_eq_true_eq_true` and related theorems below are added for
+non-confluence.  A motivating example is
+`¬((if u then b else c) = true)`.
+
+This reduces to:
+1. `¬((if u then (b = true) else (c = true))` via `ite_eq_true_distrib`
+2. `(if u then b c) = false)` via `Bool.not_eq_true`.
+
+Similar logic holds for `¬((if u then b else c) = false)` and related
+lemmas.
+-/
+
+@[simp]
+theorem not_ite_eq_true_eq_true (p : Prop) [h : Decidable p] (b c : Bool) :
+  ¬(ite p (b = true) (c = true)) ↔ (ite p (b = false) (c = false)) := by
+  cases h with | _ p => simp [p]
+
+@[simp]
+theorem not_ite_eq_false_eq_false (p : Prop) [h : Decidable p] (b c : Bool) :
+  ¬(ite p (b = false) (c = false)) ↔ (ite p (b = true) (c = true)) := by
+  cases h with | _ p => simp [p]
+
+@[simp]
+theorem not_ite_eq_true_eq_false (p : Prop) [h : Decidable p] (b c : Bool) :
+  ¬(ite p (b = true) (c = false)) ↔ (ite p (b = false) (c = true)) := by
+  cases h with | _ p => simp [p]
+
+@[simp]
+theorem not_ite_eq_false_eq_true (p : Prop) [h : Decidable p] (b c : Bool) :
+  ¬(ite p (b = false) (c = true)) ↔ (ite p (b = true) (c = false)) := by
+  cases h with | _ p => simp [p]
+
+/-
+Added for confluence between `if_true_left` and `ite_false_same` on
+`if b = true then True else b = true`
+-/
+@[simp] theorem eq_false_imp_eq_true : ∀(b:Bool), (b = false → b = true) ↔ (b = true) := by decide
+
+/-
+Added for confluence between `if_true_left` and `ite_false_same` on
+`if b = false then True else b = false`
+-/
+@[simp] theorem eq_true_imp_eq_false : ∀(b:Bool), (b = true → b = false) ↔ (b = false) := by decide
+
+
+/-! ### cond -/
+
+theorem cond_eq_ite {α} (b : Bool) (t e : α) : cond b t e = if b then t else e := by
+  cases b <;> simp
+
+theorem cond_eq_if : (bif b then x else y) = (if b then x else y) := cond_eq_ite b x y
+
+@[simp] theorem cond_not (b : Bool) (t e : α) : cond (!b) t e = cond b e t := by
+  cases b <;> rfl
+
+@[simp] theorem cond_self (c : Bool) (t : α) : cond c t t = t := by cases c <;> rfl
+
+/-
+This is a simp rule in Mathlib, but results in non-confluence that is difficult
+to fix as decide distributes over propositions. As an example, observe that
+`cond (decide (p ∧ q)) t f` could simplify to either:
+
+* `if p ∧ q then t else f` via `Bool.cond_decide` or
+* `cond (decide p && decide q) t f` via `Bool.decide_and`.
+
+A possible approach to improve normalization between `cond` and `ite` would be
+to completely simplify away `cond` by making `cond_eq_ite` a `simp` rule, but
+that has not been taken since it could surprise users to migrate pure `Bool`
+operations like `cond` to a mix of `Prop` and `Bool`.
+-/
+theorem cond_decide {α} (p : Prop) [Decidable p] (t e : α) :
+    cond (decide p) t e = if p then t else e := by
+  simp [cond_eq_ite]
+
+@[simp] theorem cond_eq_ite_iff (a : Bool) (p : Prop) [h : Decidable p] (x y u v : α) :
+  (cond a x y = ite p u v) ↔ ite a x y = ite p u v := by
+  simp [Bool.cond_eq_ite]
+
+@[simp] theorem ite_eq_cond_iff (p : Prop) [h : Decidable p] (a : Bool) (x y u v : α) :
+  (ite p x y = cond a u v) ↔ ite p x y = ite a u v := by
+  simp [Bool.cond_eq_ite]
+
+@[simp] theorem cond_eq_true_distrib : ∀(c t f : Bool),
+    (cond c t f = true) = ite (c = true) (t = true) (f = true) := by
+  decide
+
+@[simp] theorem cond_eq_false_distrib : ∀(c t f : Bool),
+    (cond c t f = false) = ite (c = true) (t = false) (f = false) := by decide
+
+protected theorem cond_true  {α : Type u} {a b : α} : cond true  a b = a := cond_true  a b
+protected theorem cond_false {α : Type u} {a b : α} : cond false a b = b := cond_false a b
+
+@[simp] theorem cond_true_left   : ∀(c f : Bool), cond c true f  = ( c || f) := by decide
+@[simp] theorem cond_false_left  : ∀(c f : Bool), cond c false f = (!c && f) := by decide
+@[simp] theorem cond_true_right  : ∀(c t : Bool), cond c t true  = (!c || t) := by decide
+@[simp] theorem cond_false_right : ∀(c t : Bool), cond c t false = ( c && t) := by decide
+
+@[simp] theorem cond_true_same  : ∀(c b : Bool), cond c c b = (c || b) := by decide
+@[simp] theorem cond_false_same : ∀(c b : Bool), cond c b c = (c && b) := by decide
+
+/-# decidability -/
+
+protected theorem decide_coe (b : Bool) [Decidable (b = true)] : decide (b = true) = b := decide_eq_true
+
+@[simp] theorem decide_and (p q : Prop) [dpq : Decidable (p ∧ q)] [dp : Decidable p] [dq : Decidable q] :
+    decide (p ∧ q) = (p && q) := by
+  cases dp with | _ p => simp [p]
+
+@[simp] theorem decide_or (p q : Prop) [dpq : Decidable (p ∨ q)] [dp : Decidable p] [dq : Decidable q] :
+    decide (p ∨ q) = (p || q) := by
+  cases dp with | _ p => simp [p]
+
+@[simp] theorem decide_iff_dist (p q : Prop) [dpq : Decidable (p ↔ q)] [dp : Decidable p] [dq : Decidable q] :
+    decide (p ↔ q) = (decide p == decide q) := by
+  cases dp with | _ p => simp [p]
+
+end Bool
+
+export Bool (cond_eq_if)
+
+/-! ### decide -/
+
+@[simp] theorem false_eq_decide_iff {p : Prop} [h : Decidable p] : false = decide p ↔ ¬p := by
+  cases h with | _ q => simp [q]
+
+@[simp] theorem true_eq_decide_iff {p : Prop} [h : Decidable p] : true = decide p ↔ p := by
+  cases h with | _ q => simp [q]

src/Init/Data/ByteArray/Basic.lean

@@ -81,7 +81,7 @@ def isEmpty (s : ByteArray) : Bool :=
   If `exact` is `false`, the capacity will be doubled when grown. -/
 @[extern "lean_byte_array_copy_slice"]
 def copySlice (src : @& ByteArray) (srcOff : Nat) (dest : ByteArray) (destOff len : Nat) (exact : Bool := true) : ByteArray :=
-  ⟨dest.data.extract 0 destOff ++ src.data.extract srcOff (srcOff + len) ++ dest.data.extract (destOff + len) dest.data.size⟩
+  ⟨dest.data.extract 0 destOff ++ src.data.extract srcOff (srcOff + len) ++ dest.data.extract (destOff + min len (src.data.size - srcOff)) dest.data.size⟩
 
 def extract (a : ByteArray) (b e : Nat) : ByteArray :=
   a.copySlice b empty 0 (e - b)

src/Init/Data/Cast.lean

@@ -0,0 +1,72 @@
+/-
+Copyright (c) 2014 Mario Carneiro. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Mario Carneiro, Gabriel Ebner
+-/
+prelude
+import Init.Coe
+
+/-!
+# `NatCast`
+
+We introduce the typeclass `NatCast R` for a type `R` with a "canonical
+homomorphism" `Nat → R`. The typeclass carries the data of the function,
+but no required axioms.
+
+This typeclass was introduced to support a uniform `simp` normal form
+for such morphisms.
+
+Without such a typeclass, we would have specific coercions such as
+`Int.ofNat`, but also later the generic coercion from `Nat` into any
+Mathlib semiring (including `Int`), and we would need to use `simp` to
+move between them. However `simp` lemmas expressed using a non-normal
+form on the LHS would then not fire.
+
+Typically different instances of this class for the same target type `R`
+are definitionally equal, and so differences in the instance do not
+block `simp` or `rw`.
+
+This logic also applies to `Int` and so we also introduce `IntCast` alongside
+`Int.
+
+## Note about coercions into arbitrary types:
+
+Coercions such as `Nat.cast` that go from a concrete structure such as
+`Nat` to an arbitrary type `R` should be set up as follows:
+```lean
+instance : CoeTail Nat R where coe := ...
+instance : CoeHTCT Nat R where coe := ...
+```
+
+It needs to be `CoeTail` instead of `Coe` because otherwise type-class
+inference would loop when constructing the transitive coercion `Nat →
+Nat → Nat → ...`. Sometimes we also need to declare the `CoeHTCT`
+instance if we need to shadow another coercion.
+-/
+
+/-- Type class for the canonical homomorphism `Nat → R`. -/
+class NatCast (R : Type u) where
+  /-- The canonical map `Nat → R`. -/
+  protected natCast : Nat → R
+
+instance : NatCast Nat where natCast n := n
+
+/--
+Canonical homomorphism from `Nat` to a type `R`.
+
+It contains just the function, with no axioms.
+In practice, the target type will likely have a (semi)ring structure,
+and this homomorphism should be a ring homomorphism.
+
+The prototypical example is `Int.ofNat`.
+
+This class and `IntCast` exist to allow different libraries with their own types that can be notated as natural numbers to have consistent `simp` normal forms without needing to create coercion simplification sets that are aware of all combinations. Libraries should make it easy to work with `NatCast` where possible. For instance, in Mathlib there will be such a homomorphism (and thus a `NatCast R` instance) whenever `R` is an additive monoid with a `1`.
+-/
+@[coe, reducible, match_pattern] protected def Nat.cast {R : Type u} [NatCast R] : Nat → R :=
+  NatCast.natCast
+
+-- see the notes about coercions into arbitrary types in the module doc-string
+instance [NatCast R] : CoeTail Nat R where coe := Nat.cast
+
+-- see the notes about coercions into arbitrary types in the module doc-string
+instance [NatCast R] : CoeHTCT Nat R where coe := Nat.cast

src/Init/Data/Channel.lean

@@ -41,7 +41,7 @@ Sends a message on an `Channel`.
 
 This function does not block.
 -/
-def Channel.send (v : α) (ch : Channel α) : BaseIO Unit :=
+def Channel.send (ch : Channel α) (v : α) : BaseIO Unit :=
   ch.atomically do
     let st ← get
     if st.closed then return

src/Init/Data/Fin.lean

@@ -6,3 +6,6 @@ Author: Leonardo de Moura
 prelude
 import Init.Data.Fin.Basic
 import Init.Data.Fin.Log2
+import Init.Data.Fin.Iterate
+import Init.Data.Fin.Fold
+import Init.Data.Fin.Lemmas

src/Init/Data/Fin/Basic.lean

@@ -1,11 +1,11 @@
 /-
 Copyright (c) 2016 Microsoft Corporation. All rights reserved.
 Released under Apache 2.0 license as described in the file LICENSE.
-Author: Leonardo de Moura
+Author: Leonardo de Moura, Robert Y. Lewis, Keeley Hoek, Mario Carneiro
 -/
 prelude
 import Init.Data.Nat.Div
-import Init.Data.Nat.Bitwise
+import Init.Data.Nat.Bitwise.Basic
 import Init.Coe
 
 open Nat
@@ -45,19 +45,19 @@ protected def sub : Fin n → Fin n → Fin n
   | ⟨a, h⟩, ⟨b, _⟩ => ⟨(a + (n - b)) % n, mlt h⟩
 
 /-!
-Remark: mod/div/modn/land/lor can be defined without using (% n), but
+Remark: land/lor can be defined without using (% n), but
 we are trying to minimize the number of Nat theorems
 needed to bootstrap Lean.
 -/
 
 protected def mod : Fin n → Fin n → Fin n
-  | ⟨a, h⟩, ⟨b, _⟩ => ⟨(a % b) % n, mlt h⟩
+  | ⟨a, h⟩, ⟨b, _⟩ => ⟨a % b,  Nat.lt_of_le_of_lt (Nat.mod_le _ _) h⟩
 
 protected def div : Fin n → Fin n → Fin n
-  | ⟨a, h⟩, ⟨b, _⟩ => ⟨(a / b) % n, mlt h⟩
+  | ⟨a, h⟩, ⟨b, _⟩ => ⟨a / b, Nat.lt_of_le_of_lt (Nat.div_le_self _ _) h⟩
 
 def modn : Fin n → Nat → Fin n
-  | ⟨a, h⟩, m => ⟨(a % m) % n, mlt h⟩
+  | ⟨a, h⟩, m => ⟨a % m, Nat.lt_of_le_of_lt (Nat.mod_le _ _) h⟩
 
 def land : Fin n → Fin n → Fin n
   | ⟨a, h⟩, ⟨b, _⟩ => ⟨(Nat.land a b) % n, mlt h⟩
@@ -100,21 +100,75 @@ instance : ShiftLeft (Fin n) where
 instance : ShiftRight (Fin n) where
   shiftRight := Fin.shiftRight
 
-instance : OfNat (Fin (no_index (n+1))) i where
+instance instOfNat : OfNat (Fin (no_index (n+1))) i where
   ofNat := Fin.ofNat i
 
 instance : Inhabited (Fin (no_index (n+1))) where
   default := 0
 
+@[simp] theorem zero_eta : (⟨0, Nat.zero_lt_succ _⟩ : Fin (n + 1)) = 0 := rfl
+
 theorem val_ne_of_ne {i j : Fin n} (h : i ≠ j) : val i ≠ val j :=
   fun h' => absurd (eq_of_val_eq h') h
 
 theorem modn_lt : ∀ {m : Nat} (i : Fin n), m > 0 → (modn i m).val < m
-  | _, ⟨_, _⟩, hp =>  Nat.lt_of_le_of_lt (mod_le _ _) (mod_lt _ hp)
+  | _, ⟨_, _⟩, hp =>  by simp [modn]; apply Nat.mod_lt; assumption
 
 theorem val_lt_of_le (i : Fin b) (h : b ≤ n) : i.val < n :=
   Nat.lt_of_lt_of_le i.isLt h
 
+protected theorem pos (i : Fin n) : 0 < n :=
+  Nat.lt_of_le_of_lt (Nat.zero_le _) i.2
+
+/-- The greatest value of `Fin (n+1)`. -/
+@[inline] def last (n : Nat) : Fin (n + 1) := ⟨n, n.lt_succ_self⟩
+
+/-- `castLT i h` embeds `i` into a `Fin` where `h` proves it belongs into.  -/
+@[inline] def castLT (i : Fin m) (h : i.1 < n) : Fin n := ⟨i.1, h⟩
+
+/-- `castLE h i` embeds `i` into a larger `Fin` type.  -/
+@[inline] def castLE (h : n ≤ m) (i : Fin n) : Fin m := ⟨i, Nat.lt_of_lt_of_le i.2 h⟩
+
+/-- `cast eq i` embeds `i` into an equal `Fin` type. -/
+@[inline] def cast (eq : n = m) (i : Fin n) : Fin m := ⟨i, eq ▸ i.2⟩
+
+/-- `castAdd m i` embeds `i : Fin n` in `Fin (n+m)`. See also `Fin.natAdd` and `Fin.addNat`. -/
+@[inline] def castAdd (m) : Fin n → Fin (n + m) :=
+  castLE <| Nat.le_add_right n m
+
+/-- `castSucc i` embeds `i : Fin n` in `Fin (n+1)`. -/
+@[inline] def castSucc : Fin n → Fin (n + 1) := castAdd 1
+
+/-- `addNat m i` adds `m` to `i`, generalizes `Fin.succ`. -/
+def addNat (i : Fin n) (m) : Fin (n + m) := ⟨i + m, Nat.add_lt_add_right i.2 _⟩
+
+/-- `natAdd n i` adds `n` to `i` "on the left". -/
+def natAdd (n) (i : Fin m) : Fin (n + m) := ⟨n + i, Nat.add_lt_add_left i.2 _⟩
+
+/-- Maps `0` to `n-1`, `1` to `n-2`, ..., `n-1` to `0`. -/
+@[inline] def rev (i : Fin n) : Fin n := ⟨n - (i + 1), Nat.sub_lt i.pos (Nat.succ_pos _)⟩
+
+/-- `subNat i h` subtracts `m` from `i`, generalizes `Fin.pred`. -/
+@[inline] def subNat (m) (i : Fin (n + m)) (h : m ≤ i) : Fin n :=
+  ⟨i - m, Nat.sub_lt_right_of_lt_add h i.2⟩
+
+/-- Predecessor of a nonzero element of `Fin (n+1)`. -/
+@[inline] def pred {n : Nat} (i : Fin (n + 1)) (h : i ≠ 0) : Fin n :=
+  subNat 1 i <| Nat.pos_of_ne_zero <| mt (Fin.eq_of_val_eq (j := 0)) h
+
+theorem val_inj {a b : Fin n} : a.1 = b.1 ↔ a = b := ⟨Fin.eq_of_val_eq, Fin.val_eq_of_eq⟩
+
+theorem val_congr {n : Nat} {a b : Fin n} (h : a = b) : (a : Nat) = (b : Nat) :=
+  Fin.val_inj.mpr h
+
+theorem val_le_of_le {n : Nat} {a b : Fin n} (h : a ≤ b) : (a : Nat) ≤ (b : Nat) := h
+
+theorem val_le_of_ge {n : Nat} {a b : Fin n} (h : a ≥ b) : (b : Nat) ≤ (a : Nat) := h
+
+theorem val_add_one_le_of_lt {n : Nat} {a b : Fin n} (h : a < b) : (a : Nat) + 1 ≤ (b : Nat) := h
+
+theorem val_add_one_le_of_gt {n : Nat} {a b : Fin n} (h : a > b) : (b : Nat) + 1 ≤ (a : Nat) := h
+
 end Fin
 
 instance [GetElem cont Nat elem dom] : GetElem cont (Fin n) elem fun xs i => dom xs i where

src/Init/Data/Fin/Fold.lean

@@ -0,0 +1,21 @@
+/-
+Copyright (c) 2023 François G. Dorais. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: François G. Dorais
+-/
+prelude
+import Init.Data.Nat.Linear
+
+/-- Folds over `Fin n` from the left: `foldl 3 f x = f (f (f x 0) 1) 2`. -/
+@[inline] def foldl (n) (f : α → Fin n → α) (init : α) : α := loop init 0 where
+  /-- Inner loop for `Fin.foldl`. `Fin.foldl.loop n f x i = f (f (f x i) ...) (n-1)`  -/
+  loop (x : α) (i : Nat) : α :=
+    if h : i < n then loop (f x ⟨i, h⟩) (i+1) else x
+  termination_by n - i
+
+/-- Folds over `Fin n` from the right: `foldr 3 f x = f 0 (f 1 (f 2 x))`. -/
+@[inline] def foldr (n) (f : Fin n → α → α) (init : α) : α := loop ⟨n, Nat.le_refl n⟩ init where
+  /-- Inner loop for `Fin.foldr`. `Fin.foldr.loop n f i x = f 0 (f ... (f (i-1) x))`  -/
+  loop : {i // i ≤ n} → α → α
+  | ⟨0, _⟩, x => x
+  | ⟨i+1, h⟩, x => loop ⟨i, Nat.le_of_lt h⟩ (f ⟨i, h⟩ x)

src/Init/Data/Fin/Iterate.lean

@@ -0,0 +1,95 @@
+/-
+Copyright (c) 2024 Lean FRO, LLC. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Joe Hendrix
+-/
+prelude
+import Init.PropLemmas
+import Init.Data.Fin.Basic
+
+namespace Fin
+
+/--
+`hIterateFrom f i bnd a` applies `f` over indices `[i:n]` to compute `P n`
+from `P i`.
+
+See `hIterate` below for more details.
+-/
+def hIterateFrom (P : Nat → Sort _) {n} (f : ∀(i : Fin n), P i.val → P (i.val+1))
+      (i : Nat) (ubnd : i ≤ n) (a : P i) : P n :=
+  if g : i < n then
+    hIterateFrom P f (i+1) g (f ⟨i, g⟩ a)
+  else
+    have p : i = n := (or_iff_left g).mp (Nat.eq_or_lt_of_le ubnd)
+    _root_.cast (congrArg P p) a
+  termination_by n - i
+
+/--
+`hIterate` is a heterogenous iterative operation that applies a
+index-dependent function `f` to a value `init : P start` a total of
+`stop - start` times to produce a value of type `P stop`.
+
+Concretely, `hIterate start stop f init` is equal to
+```lean
+  init |> f start _ |> f (start+1) _ ... |> f (end-1) _
+```
+
+Because it is heterogenous and must return a value of type `P stop`,
+`hIterate` requires proof that `start ≤ stop`.
+
+One can prove properties of `hIterate` using the general theorem
+`hIterate_elim` or other more specialized theorems.
+ -/
+def hIterate (P : Nat → Sort _) {n : Nat} (init : P 0) (f : ∀(i : Fin n), P i.val → P (i.val+1)) :
+    P n :=
+  hIterateFrom P f 0 (Nat.zero_le n) init
+
+private theorem hIterateFrom_elim {P : Nat → Sort _}(Q : ∀(i : Nat), P i → Prop)
+    {n  : Nat}
+    (f : ∀(i : Fin n), P i.val → P (i.val+1))
+    {i : Nat} (ubnd : i ≤ n)
+    (s : P i)
+    (init : Q i s)
+    (step : ∀(k : Fin n) (s : P k.val), Q k.val s → Q (k.val+1) (f k s)) :
+    Q n (hIterateFrom P f i ubnd s) := by
+  let ⟨j, p⟩ := Nat.le.dest ubnd
+  induction j generalizing i ubnd init with
+  | zero =>
+    unfold hIterateFrom
+    have g : ¬ (i < n) := by simp at p; simp [p]
+    have r : Q n (_root_.cast (congrArg P p) s) :=
+      @Eq.rec Nat i (fun k eq => Q k (_root_.cast (congrArg P eq) s)) init n p
+    simp only [g, r, dite_false]
+  | succ j inv =>
+    unfold hIterateFrom
+    have d : Nat.succ i + j = n := by simp [Nat.succ_add]; exact p
+    have g : i < n := Nat.le.intro d
+    simp only [g]
+    exact inv _ _ (step ⟨i,g⟩ s init) d
+
+/-
+`hIterate_elim` provides a mechanism for showing that the result of
+`hIterate` satisifies a property `Q stop` by showing that the states
+at the intermediate indices `i : start ≤ i < stop` satisfy `Q i`.
+-/
+theorem hIterate_elim {P : Nat → Sort _} (Q : ∀(i : Nat), P i → Prop)
+    {n : Nat} (f : ∀(i : Fin n), P i.val → P (i.val+1)) (s : P 0) (init : Q 0 s)
+    (step : ∀(k : Fin n) (s : P k.val), Q k.val s → Q (k.val+1) (f k s)) :
+    Q n (hIterate P s f) := by
+  exact hIterateFrom_elim _ _ _ _ init step
+
+/-
+`hIterate_eq`provides a mechanism for replacing `hIterate P s f` with a
+function `state` showing that matches the steps performed by `hIterate`.
+
+This allows rewriting incremental code using `hIterate` with a
+non-incremental state function.
+-/
+theorem hIterate_eq {P : Nat → Sort _} (state : ∀(i : Nat), P i)
+    {n : Nat} (f : ∀(i : Fin n), P i.val → P (i.val+1)) (s : P 0)
+    (init : s = state 0)
+    (step : ∀(i : Fin n), f i (state i) = state (i+1)) :
+    hIterate P s f = state n := by
+  apply hIterate_elim (fun i s => s = state i) f s init
+  intro i s s_eq
+  simp only [s_eq, step]

src/Init/Data/Fin/Lemmas.lean

@@ -0,0 +1,834 @@
+/-
+Copyright (c) 2022 Mario Carneiro. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Mario Carneiro
+-/
+prelude
+import Init.Data.Fin.Basic
+import Init.Data.Nat.Lemmas
+import Init.Ext
+import Init.ByCases
+import Init.Conv
+import Init.Omega
+
+namespace Fin
+
+/-- If you actually have an element of `Fin n`, then the `n` is always positive -/
+theorem size_pos (i : Fin n) : 0 < n := Nat.lt_of_le_of_lt (Nat.zero_le _) i.2
+
+theorem mod_def (a m : Fin n) : a % m = Fin.mk (a % m) (Nat.lt_of_le_of_lt (Nat.mod_le _ _) a.2) :=
+  rfl
+
+theorem mul_def (a b : Fin n) : a * b = Fin.mk ((a * b) % n) (Nat.mod_lt _ a.size_pos) := rfl
+
+theorem sub_def (a b : Fin n) : a - b = Fin.mk ((a + (n - b)) % n) (Nat.mod_lt _ a.size_pos) := rfl
+
+theorem size_pos' : ∀ [Nonempty (Fin n)], 0 < n | ⟨i⟩ => i.size_pos
+
+@[simp] theorem is_lt (a : Fin n) : (a : Nat) < n := a.2
+
+theorem pos_iff_nonempty {n : Nat} : 0 < n ↔ Nonempty (Fin n) :=
+  ⟨fun h => ⟨⟨0, h⟩⟩, fun ⟨i⟩ => i.pos⟩
+
+/-! ### coercions and constructions -/
+
+@[simp] protected theorem eta (a : Fin n) (h : a < n) : (⟨a, h⟩ : Fin n) = a := rfl
+
+@[ext] theorem ext {a b : Fin n} (h : (a : Nat) = b) : a = b := eq_of_val_eq h
+
+theorem ext_iff {a b : Fin n} : a = b ↔ a.1 = b.1 := val_inj.symm
+
+theorem val_ne_iff {a b : Fin n} : a.1 ≠ b.1 ↔ a ≠ b := not_congr val_inj
+
+theorem exists_iff {p : Fin n → Prop} : (∃ i, p i) ↔ ∃ i h, p ⟨i, h⟩ :=
+  ⟨fun ⟨⟨i, hi⟩, hpi⟩ => ⟨i, hi, hpi⟩, fun ⟨i, hi, hpi⟩ => ⟨⟨i, hi⟩, hpi⟩⟩
+
+theorem forall_iff {p : Fin n → Prop} : (∀ i, p i) ↔ ∀ i h, p ⟨i, h⟩ :=
+  ⟨fun h i hi => h ⟨i, hi⟩, fun h ⟨i, hi⟩ => h i hi⟩
+
+protected theorem mk.inj_iff {n a b : Nat} {ha : a < n} {hb : b < n} :
+    (⟨a, ha⟩ : Fin n) = ⟨b, hb⟩ ↔ a = b := ext_iff
+
+theorem val_mk {m n : Nat} (h : m < n) : (⟨m, h⟩ : Fin n).val = m := rfl
+
+theorem eq_mk_iff_val_eq {a : Fin n} {k : Nat} {hk : k < n} :
+    a = ⟨k, hk⟩ ↔ (a : Nat) = k := ext_iff
+
+theorem mk_val (i : Fin n) : (⟨i, i.isLt⟩ : Fin n) = i := Fin.eta ..
+
+@[simp] theorem val_ofNat' (a : Nat) (is_pos : n > 0) :
+  (Fin.ofNat' a is_pos).val = a % n := rfl
+
+@[deprecated ofNat'_zero_val] theorem ofNat'_zero_val : (Fin.ofNat' 0 h).val = 0 := Nat.zero_mod _
+
+@[simp] theorem mod_val (a b : Fin n) : (a % b).val = a.val % b.val :=
+  rfl
+
+@[simp] theorem div_val (a b : Fin n) : (a / b).val = a.val / b.val :=
+  rfl
+
+@[simp] theorem modn_val (a : Fin n) (b : Nat) : (a.modn b).val = a.val % b :=
+  rfl
+
+theorem ite_val {n : Nat} {c : Prop} [Decidable c] {x : c → Fin n} (y : ¬c → Fin n) :
+    (if h : c then x h else y h).val = if h : c then (x h).val else (y h).val := by
+  by_cases c <;> simp [*]
+
+theorem dite_val {n : Nat} {c : Prop} [Decidable c] {x y : Fin n} :
+    (if c then x else y).val = if c then x.val else y.val := by
+  by_cases c <;> simp [*]
+
+/-! ### order -/
+
+theorem le_def {a b : Fin n} : a ≤ b ↔ a.1 ≤ b.1 := .rfl
+
+theorem lt_def {a b : Fin n} : a < b ↔ a.1 < b.1 := .rfl
+
+theorem lt_iff_val_lt_val {a b : Fin n} : a < b ↔ a.val < b.val := Iff.rfl
+
+@[simp] protected theorem not_le {a b : Fin n} : ¬ a ≤ b ↔ b < a := Nat.not_le
+
+@[simp] protected theorem not_lt {a b : Fin n} : ¬ a < b ↔ b ≤ a := Nat.not_lt
+
+protected theorem ne_of_lt {a b : Fin n} (h : a < b) : a ≠ b := Fin.ne_of_val_ne (Nat.ne_of_lt h)
+
+protected theorem ne_of_gt {a b : Fin n} (h : a < b) : b ≠ a := Fin.ne_of_val_ne (Nat.ne_of_gt h)
+
+protected theorem le_of_lt {a b : Fin n} (h : a < b) : a ≤ b := Nat.le_of_lt h
+
+theorem is_le (i : Fin (n + 1)) : i ≤ n := Nat.le_of_lt_succ i.is_lt
+
+@[simp] theorem is_le' {a : Fin n} : a ≤ n := Nat.le_of_lt a.is_lt
+
+theorem mk_lt_of_lt_val {b : Fin n} {a : Nat} (h : a < b) :
+    (⟨a, Nat.lt_trans h b.is_lt⟩ : Fin n) < b := h
+
+theorem mk_le_of_le_val {b : Fin n} {a : Nat} (h : a ≤ b) :
+    (⟨a, Nat.lt_of_le_of_lt h b.is_lt⟩ : Fin n) ≤ b := h
+
+@[simp] theorem mk_le_mk {x y : Nat} {hx hy} : (⟨x, hx⟩ : Fin n) ≤ ⟨y, hy⟩ ↔ x ≤ y := .rfl
+
+@[simp] theorem mk_lt_mk {x y : Nat} {hx hy} : (⟨x, hx⟩ : Fin n) < ⟨y, hy⟩ ↔ x < y := .rfl
+
+@[simp] theorem val_zero (n : Nat) : (0 : Fin (n + 1)).1 = 0 := rfl
+
+@[simp] theorem mk_zero : (⟨0, Nat.succ_pos n⟩ : Fin (n + 1)) = 0 := rfl
+
+@[simp] theorem zero_le (a : Fin (n + 1)) : 0 ≤ a := Nat.zero_le a.val
+
+theorem zero_lt_one : (0 : Fin (n + 2)) < 1 := Nat.zero_lt_one
+
+@[simp] theorem not_lt_zero (a : Fin (n + 1)) : ¬a < 0 := nofun
+
+theorem pos_iff_ne_zero {a : Fin (n + 1)} : 0 < a ↔ a ≠ 0 := by
+  rw [lt_def, val_zero, Nat.pos_iff_ne_zero, ← val_ne_iff]; rfl
+
+theorem eq_zero_or_eq_succ {n : Nat} : ∀ i : Fin (n + 1), i = 0 ∨ ∃ j : Fin n, i = j.succ
+  | 0 => .inl rfl
+  | ⟨j + 1, h⟩ => .inr ⟨⟨j, Nat.lt_of_succ_lt_succ h⟩, rfl⟩
+
+theorem eq_succ_of_ne_zero {n : Nat} {i : Fin (n + 1)} (hi : i ≠ 0) : ∃ j : Fin n, i = j.succ :=
+  (eq_zero_or_eq_succ i).resolve_left hi
+
+@[simp] theorem val_rev (i : Fin n) : rev i = n - (i + 1) := rfl
+
+@[simp] theorem rev_rev (i : Fin n) : rev (rev i) = i := ext <| by
+  rw [val_rev, val_rev, ← Nat.sub_sub, Nat.sub_sub_self (by exact i.2), Nat.add_sub_cancel]
+
+@[simp] theorem rev_le_rev {i j : Fin n} : rev i ≤ rev j ↔ j ≤ i := by
+  simp only [le_def, val_rev, Nat.sub_le_sub_iff_left (Nat.succ_le.2 j.is_lt)]
+  exact Nat.succ_le_succ_iff
+
+@[simp] theorem rev_inj {i j : Fin n} : rev i = rev j ↔ i = j :=
+  ⟨fun h => by simpa using congrArg rev h, congrArg _⟩
+
+theorem rev_eq {n a : Nat} (i : Fin (n + 1)) (h : n = a + i) :
+    rev i = ⟨a, Nat.lt_succ_of_le (h ▸ Nat.le_add_right ..)⟩ := by
+  ext; dsimp
+  conv => lhs; congr; rw [h]
+  rw [Nat.add_assoc, Nat.add_sub_cancel]
+
+@[simp] theorem rev_lt_rev {i j : Fin n} : rev i < rev j ↔ j < i := by
+  rw [← Fin.not_le, ← Fin.not_le, rev_le_rev]
+
+@[simp] theorem val_last (n : Nat) : last n = n := rfl
+
+theorem le_last (i : Fin (n + 1)) : i ≤ last n := Nat.le_of_lt_succ i.is_lt
+
+theorem last_pos : (0 : Fin (n + 2)) < last (n + 1) := Nat.succ_pos _
+
+theorem eq_last_of_not_lt {i : Fin (n + 1)} (h : ¬(i : Nat) < n) : i = last n :=
+  ext <| Nat.le_antisymm (le_last i) (Nat.not_lt.1 h)
+
+theorem val_lt_last {i : Fin (n + 1)} : i ≠ last n → (i : Nat) < n :=
+  Decidable.not_imp_comm.1 eq_last_of_not_lt
+
+@[simp] theorem rev_last (n : Nat) : rev (last n) = 0 := ext <| by simp
+
+@[simp] theorem rev_zero (n : Nat) : rev 0 = last n := by
+  rw [← rev_rev (last _), rev_last]
+
+/-! ### addition, numerals, and coercion from Nat -/
+
+@[simp] theorem val_one (n : Nat) : (1 : Fin (n + 2)).val = 1 := rfl
+
+@[simp] theorem mk_one : (⟨1, Nat.succ_lt_succ (Nat.succ_pos n)⟩ : Fin (n + 2)) = (1 : Fin _) := rfl
+
+theorem subsingleton_iff_le_one : Subsingleton (Fin n) ↔ n ≤ 1 := by
+  (match n with | 0 | 1 | n+2 => ?_) <;> try simp
+  · exact ⟨nofun⟩
+  · exact ⟨fun ⟨0, _⟩ ⟨0, _⟩ => rfl⟩
+  · exact iff_of_false (fun h => Fin.ne_of_lt zero_lt_one (h.elim ..)) (of_decide_eq_false rfl)
+
+instance subsingleton_zero : Subsingleton (Fin 0) := subsingleton_iff_le_one.2 (by decide)
+
+instance subsingleton_one : Subsingleton (Fin 1) := subsingleton_iff_le_one.2 (by decide)
+
+theorem fin_one_eq_zero (a : Fin 1) : a = 0 := Subsingleton.elim a 0
+
+theorem add_def (a b : Fin n) : a + b = Fin.mk ((a + b) % n) (Nat.mod_lt _ a.size_pos) := rfl
+
+theorem val_add (a b : Fin n) : (a + b).val = (a.val + b.val) % n := rfl
+
+theorem val_add_one_of_lt {n : Nat} {i : Fin n.succ} (h : i < last _) : (i + 1).1 = i + 1 := by
+  match n with
+  | 0 => cases h
+  | n+1 => rw [val_add, val_one, Nat.mod_eq_of_lt (by exact Nat.succ_lt_succ h)]
+
+@[simp] theorem last_add_one : ∀ n, last n + 1 = 0
+  | 0 => rfl
+  | n + 1 => by ext; rw [val_add, val_zero, val_last, val_one, Nat.mod_self]
+
+theorem val_add_one {n : Nat} (i : Fin (n + 1)) :
+    ((i + 1 : Fin (n + 1)) : Nat) = if i = last _ then (0 : Nat) else i + 1 := by
+  match Nat.eq_or_lt_of_le (le_last i) with
+  | .inl h => cases Fin.eq_of_val_eq h; simp
+  | .inr h => simpa [Fin.ne_of_lt h] using val_add_one_of_lt h
+
+@[simp] theorem val_two {n : Nat} : (2 : Fin (n + 3)).val = 2 := rfl
+
+theorem add_one_pos (i : Fin (n + 1)) (h : i < Fin.last n) : (0 : Fin (n + 1)) < i + 1 := by
+  match n with
+  | 0 => cases h
+  | n+1 =>
+    rw [Fin.lt_def, val_last, ← Nat.add_lt_add_iff_right] at h
+    rw [Fin.lt_def, val_add, val_zero, val_one, Nat.mod_eq_of_lt h]
+    exact Nat.zero_lt_succ _
+
+theorem one_pos : (0 : Fin (n + 2)) < 1 := Nat.succ_pos 0
+
+theorem zero_ne_one : (0 : Fin (n + 2)) ≠ 1 := Fin.ne_of_lt one_pos
+
+/-! ### succ and casts into larger Fin types -/
+
+@[simp] theorem val_succ (j : Fin n) : (j.succ : Nat) = j + 1 := rfl
+
+@[simp] theorem succ_pos (a : Fin n) : (0 : Fin (n + 1)) < a.succ := by
+  simp [Fin.lt_def, Nat.succ_pos]
+
+@[simp] theorem succ_le_succ_iff {a b : Fin n} : a.succ ≤ b.succ ↔ a ≤ b := Nat.succ_le_succ_iff
+
+@[simp] theorem succ_lt_succ_iff {a b : Fin n} : a.succ < b.succ ↔ a < b := Nat.succ_lt_succ_iff
+
+@[simp] theorem succ_inj {a b : Fin n} : a.succ = b.succ ↔ a = b := by
+  refine ⟨fun h => ext ?_, congrArg _⟩
+  apply Nat.le_antisymm <;> exact succ_le_succ_iff.1 (h ▸ Nat.le_refl _)
+
+theorem succ_ne_zero {n} : ∀ k : Fin n, Fin.succ k ≠ 0
+  | ⟨k, _⟩, heq => Nat.succ_ne_zero k <| ext_iff.1 heq
+
+@[simp] theorem succ_zero_eq_one : Fin.succ (0 : Fin (n + 1)) = 1 := rfl
+
+/-- Version of `succ_one_eq_two` to be used by `dsimp` -/
+@[simp] theorem succ_one_eq_two : Fin.succ (1 : Fin (n + 2)) = 2 := rfl
+
+@[simp] theorem succ_mk (n i : Nat) (h : i < n) :
+    Fin.succ ⟨i, h⟩ = ⟨i + 1, Nat.succ_lt_succ h⟩ := rfl
+
+theorem mk_succ_pos (i : Nat) (h : i < n) :
+    (0 : Fin (n + 1)) < ⟨i.succ, Nat.add_lt_add_right h 1⟩ := by
+  rw [lt_def, val_zero]; exact Nat.succ_pos i
+
+theorem one_lt_succ_succ (a : Fin n) : (1 : Fin (n + 2)) < a.succ.succ := by
+  let n+1 := n
+  rw [← succ_zero_eq_one, succ_lt_succ_iff]; exact succ_pos a
+
+@[simp] theorem add_one_lt_iff {n : Nat} {k : Fin (n + 2)} : k + 1 < k ↔ k = last _ := by
+  simp only [lt_def, val_add, val_last, ext_iff]
+  let ⟨k, hk⟩ := k
+  match Nat.eq_or_lt_of_le (Nat.le_of_lt_succ hk) with
+  | .inl h => cases h; simp [Nat.succ_pos]
+  | .inr hk' => simp [Nat.ne_of_lt hk', Nat.mod_eq_of_lt (Nat.succ_lt_succ hk'), Nat.le_succ]
+
+@[simp] theorem add_one_le_iff {n : Nat} : ∀ {k : Fin (n + 1)}, k + 1 ≤ k ↔ k = last _ := by
+  match n with
+  | 0 =>
+    intro (k : Fin 1)
+    exact iff_of_true (Subsingleton.elim (α := Fin 1) (k+1) _ ▸ Nat.le_refl _) (fin_one_eq_zero ..)
+  | n + 1 =>
+    intro (k : Fin (n+2))
+    rw [← add_one_lt_iff, lt_def, le_def, Nat.lt_iff_le_and_ne, and_iff_left]
+    rw [val_add_one]
+    split <;> simp [*, (Nat.succ_ne_zero _).symm, Nat.ne_of_gt (Nat.lt_succ_self _)]
+
+@[simp] theorem last_le_iff {n : Nat} {k : Fin (n + 1)} : last n ≤ k ↔ k = last n := by
+  rw [ext_iff, Nat.le_antisymm_iff, le_def, and_iff_right (by apply le_last)]
+
+@[simp] theorem lt_add_one_iff {n : Nat} {k : Fin (n + 1)} : k < k + 1 ↔ k < last n := by
+  rw [← Decidable.not_iff_not]; simp
+
+@[simp] theorem le_zero_iff {n : Nat} {k : Fin (n + 1)} : k ≤ 0 ↔ k = 0 :=
+  ⟨fun h => Fin.eq_of_val_eq <| Nat.eq_zero_of_le_zero h, (· ▸ Nat.le_refl _)⟩
+
+theorem succ_succ_ne_one (a : Fin n) : Fin.succ (Fin.succ a) ≠ 1 :=
+  Fin.ne_of_gt (one_lt_succ_succ a)
+
+@[simp] theorem coe_castLT (i : Fin m) (h : i.1 < n) : (castLT i h : Nat) = i := rfl
+
+@[simp] theorem castLT_mk (i n m : Nat) (hn : i < n) (hm : i < m) : castLT ⟨i, hn⟩ hm = ⟨i, hm⟩ :=
+  rfl
+
+@[simp] theorem coe_castLE (h : n ≤ m) (i : Fin n) : (castLE h i : Nat) = i := rfl
+
+@[simp] theorem castLE_mk (i n m : Nat) (hn : i < n) (h : n ≤ m) :
+    castLE h ⟨i, hn⟩ = ⟨i, Nat.lt_of_lt_of_le hn h⟩ := rfl
+
+@[simp] theorem castLE_zero {n m : Nat} (h : n.succ ≤ m.succ) : castLE h 0 = 0 := by simp [ext_iff]
+
+@[simp] theorem castLE_succ {m n : Nat} (h : m + 1 ≤ n + 1) (i : Fin m) :
+    castLE h i.succ = (castLE (Nat.succ_le_succ_iff.mp h) i).succ := by simp [ext_iff]
+
+@[simp] theorem castLE_castLE {k m n} (km : k ≤ m) (mn : m ≤ n) (i : Fin k) :
+    Fin.castLE mn (Fin.castLE km i) = Fin.castLE (Nat.le_trans km mn) i :=
+  Fin.ext (by simp only [coe_castLE])
+
+@[simp] theorem castLE_comp_castLE {k m n} (km : k ≤ m) (mn : m ≤ n) :
+    Fin.castLE mn ∘ Fin.castLE km = Fin.castLE (Nat.le_trans km mn) :=
+  funext (castLE_castLE km mn)
+
+@[simp] theorem coe_cast (h : n = m) (i : Fin n) : (cast h i : Nat) = i := rfl
+
+@[simp] theorem cast_last {n' : Nat} {h : n + 1 = n' + 1} : cast h (last n) = last n' :=
+  ext (by rw [coe_cast, val_last, val_last, Nat.succ.inj h])
+
+@[simp] theorem cast_mk (h : n = m) (i : Nat) (hn : i < n) : cast h ⟨i, hn⟩ = ⟨i, h ▸ hn⟩ := rfl
+
+@[simp] theorem cast_trans {k : Nat} (h : n = m) (h' : m = k) {i : Fin n} :
+    cast h' (cast h i) = cast (Eq.trans h h') i := rfl
+
+theorem castLE_of_eq {m n : Nat} (h : m = n) {h' : m ≤ n} : castLE h' = Fin.cast h := rfl
+
+@[simp] theorem coe_castAdd (m : Nat) (i : Fin n) : (castAdd m i : Nat) = i := rfl
+
+@[simp] theorem castAdd_zero : (castAdd 0 : Fin n → Fin (n + 0)) = cast rfl := rfl
+
+theorem castAdd_lt {m : Nat} (n : Nat) (i : Fin m) : (castAdd n i : Nat) < m := by simp
+
+@[simp] theorem castAdd_mk (m : Nat) (i : Nat) (h : i < n) :
+    castAdd m ⟨i, h⟩ = ⟨i, Nat.lt_add_right m h⟩ := rfl
+
+@[simp] theorem castAdd_castLT (m : Nat) (i : Fin (n + m)) (hi : i.val < n) :
+    castAdd m (castLT i hi) = i := rfl
+
+@[simp] theorem castLT_castAdd (m : Nat) (i : Fin n) :
+    castLT (castAdd m i) (castAdd_lt m i) = i := rfl
+
+/-- For rewriting in the reverse direction, see `Fin.cast_castAdd_left`. -/
+theorem castAdd_cast {n n' : Nat} (m : Nat) (i : Fin n') (h : n' = n) :
+    castAdd m (Fin.cast h i) = Fin.cast (congrArg (. + m) h) (castAdd m i) := ext rfl
+
+theorem cast_castAdd_left {n n' m : Nat} (i : Fin n') (h : n' + m = n + m) :
+    cast h (castAdd m i) = castAdd m (cast (Nat.add_right_cancel h) i) := rfl
+
+@[simp] theorem cast_castAdd_right {n m m' : Nat} (i : Fin n) (h : n + m' = n + m) :
+    cast h (castAdd m' i) = castAdd m i := rfl
+
+theorem castAdd_castAdd {m n p : Nat} (i : Fin m) :
+    castAdd p (castAdd n i) = cast (Nat.add_assoc ..).symm (castAdd (n + p) i) := rfl
+
+/-- The cast of the successor is the successor of the cast. See `Fin.succ_cast_eq` for rewriting in
+the reverse direction. -/
+@[simp] theorem cast_succ_eq {n' : Nat} (i : Fin n) (h : n.succ = n'.succ) :
+    cast h i.succ = (cast (Nat.succ.inj h) i).succ := rfl
+
+theorem succ_cast_eq {n' : Nat} (i : Fin n) (h : n = n') :
+    (cast h i).succ = cast (by rw [h]) i.succ := rfl
+
+@[simp] theorem coe_castSucc (i : Fin n) : (Fin.castSucc i : Nat) = i := rfl
+
+@[simp] theorem castSucc_mk (n i : Nat) (h : i < n) : castSucc ⟨i, h⟩ = ⟨i, Nat.lt.step h⟩ := rfl
+
+@[simp] theorem cast_castSucc {n' : Nat} {h : n + 1 = n' + 1} {i : Fin n} :
+    cast h (castSucc i) = castSucc (cast (Nat.succ.inj h) i) := rfl
+
+theorem castSucc_lt_succ (i : Fin n) : Fin.castSucc i < i.succ :=
+  lt_def.2 <| by simp only [coe_castSucc, val_succ, Nat.lt_succ_self]
+
+theorem le_castSucc_iff {i : Fin (n + 1)} {j : Fin n} : i ≤ Fin.castSucc j ↔ i < j.succ := by
+  simpa [lt_def, le_def] using Nat.succ_le_succ_iff.symm
+
+theorem castSucc_lt_iff_succ_le {n : Nat} {i : Fin n} {j : Fin (n + 1)} :
+    Fin.castSucc i < j ↔ i.succ ≤ j := .rfl
+
+@[simp] theorem succ_last (n : Nat) : (last n).succ = last n.succ := rfl
+
+@[simp] theorem succ_eq_last_succ {n : Nat} (i : Fin n.succ) :
+    i.succ = last (n + 1) ↔ i = last n := by rw [← succ_last, succ_inj]
+
+@[simp] theorem castSucc_castLT (i : Fin (n + 1)) (h : (i : Nat) < n) :
+    castSucc (castLT i h) = i := rfl
+
+@[simp] theorem castLT_castSucc {n : Nat} (a : Fin n) (h : (a : Nat) < n) :
+    castLT (castSucc a) h = a := rfl
+
+@[simp] theorem castSucc_lt_castSucc_iff {a b : Fin n} :
+    Fin.castSucc a < Fin.castSucc b ↔ a < b := .rfl
+
+theorem castSucc_inj {a b : Fin n} : castSucc a = castSucc b ↔ a = b := by simp [ext_iff]
+
+theorem castSucc_lt_last (a : Fin n) : castSucc a < last n := a.is_lt
+
+@[simp] theorem castSucc_zero : castSucc (0 : Fin (n + 1)) = 0 := rfl
+
+@[simp] theorem castSucc_one {n : Nat} : castSucc (1 : Fin (n + 2)) = 1 := rfl
+
+/-- `castSucc i` is positive when `i` is positive -/
+theorem castSucc_pos {i : Fin (n + 1)} (h : 0 < i) : 0 < castSucc i := by
+  simpa [lt_def] using h
+
+@[simp] theorem castSucc_eq_zero_iff (a : Fin (n + 1)) : castSucc a = 0 ↔ a = 0 := by simp [ext_iff]
+
+theorem castSucc_ne_zero_iff (a : Fin (n + 1)) : castSucc a ≠ 0 ↔ a ≠ 0 :=
+  not_congr <| castSucc_eq_zero_iff a
+
+theorem castSucc_fin_succ (n : Nat) (j : Fin n) :
+    castSucc (Fin.succ j) = Fin.succ (castSucc j) := by simp [Fin.ext_iff]
+
+@[simp]
+theorem coeSucc_eq_succ {a : Fin n} : castSucc a + 1 = a.succ := by
+  cases n
+  · exact a.elim0
+  · simp [ext_iff, add_def, Nat.mod_eq_of_lt (Nat.succ_lt_succ a.is_lt)]
+
+theorem lt_succ {a : Fin n} : castSucc a < a.succ := by
+  rw [castSucc, lt_def, coe_castAdd, val_succ]; exact Nat.lt_succ_self a.val
+
+theorem exists_castSucc_eq {n : Nat} {i : Fin (n + 1)} : (∃ j, castSucc j = i) ↔ i ≠ last n :=
+  ⟨fun ⟨j, hj⟩ => hj ▸ Fin.ne_of_lt j.castSucc_lt_last,
+   fun hi => ⟨i.castLT <| Fin.val_lt_last hi, rfl⟩⟩
+
+theorem succ_castSucc {n : Nat} (i : Fin n) : i.castSucc.succ = castSucc i.succ := rfl
+
+@[simp] theorem coe_addNat (m : Nat) (i : Fin n) : (addNat i m : Nat) = i + m := rfl
+
+@[simp] theorem addNat_one {i : Fin n} : addNat i 1 = i.succ := rfl
+
+theorem le_coe_addNat (m : Nat) (i : Fin n) : m ≤ addNat i m :=
+  Nat.le_add_left _ _
+
+@[simp] theorem addNat_mk (n i : Nat) (hi : i < m) :
+    addNat ⟨i, hi⟩ n = ⟨i + n, Nat.add_lt_add_right hi n⟩ := rfl
+
+@[simp] theorem cast_addNat_zero {n n' : Nat} (i : Fin n) (h : n + 0 = n') :
+    cast h (addNat i 0) = cast ((Nat.add_zero _).symm.trans h) i := rfl
+
+/-- For rewriting in the reverse direction, see `Fin.cast_addNat_left`. -/
+theorem addNat_cast {n n' m : Nat} (i : Fin n') (h : n' = n) :
+    addNat (cast h i) m = cast (congrArg (. + m) h) (addNat i m) := rfl
+
+theorem cast_addNat_left {n n' m : Nat} (i : Fin n') (h : n' + m = n + m) :
+    cast h (addNat i m) = addNat (cast (Nat.add_right_cancel h) i) m := rfl
+
+@[simp] theorem cast_addNat_right {n m m' : Nat} (i : Fin n) (h : n + m' = n + m) :
+    cast h (addNat i m') = addNat i m :=
+  ext <| (congrArg ((· + ·) (i : Nat)) (Nat.add_left_cancel h) : _)
+
+@[simp] theorem coe_natAdd (n : Nat) {m : Nat} (i : Fin m) : (natAdd n i : Nat) = n + i := rfl
+
+@[simp] theorem natAdd_mk (n i : Nat) (hi : i < m) :
+    natAdd n ⟨i, hi⟩ = ⟨n + i, Nat.add_lt_add_left hi n⟩ := rfl
+
+theorem le_coe_natAdd (m : Nat) (i : Fin n) : m ≤ natAdd m i := Nat.le_add_right ..
+
+theorem natAdd_zero {n : Nat} : natAdd 0 = cast (Nat.zero_add n).symm := by ext; simp
+
+/-- For rewriting in the reverse direction, see `Fin.cast_natAdd_right`. -/
+theorem natAdd_cast {n n' : Nat} (m : Nat) (i : Fin n') (h : n' = n) :
+    natAdd m (cast h i) = cast (congrArg _ h) (natAdd m i) := rfl
+
+theorem cast_natAdd_right {n n' m : Nat} (i : Fin n') (h : m + n' = m + n) :
+    cast h (natAdd m i) = natAdd m (cast (Nat.add_left_cancel h) i) := rfl
+
+@[simp] theorem cast_natAdd_left {n m m' : Nat} (i : Fin n) (h : m' + n = m + n) :
+    cast h (natAdd m' i) = natAdd m i :=
+  ext <| (congrArg (· + (i : Nat)) (Nat.add_right_cancel h) : _)
+
+theorem castAdd_natAdd (p m : Nat) {n : Nat} (i : Fin n) :
+    castAdd p (natAdd m i) = cast (Nat.add_assoc ..).symm (natAdd m (castAdd p i)) := rfl
+
+theorem natAdd_castAdd (p m : Nat) {n : Nat} (i : Fin n) :
+    natAdd m (castAdd p i) = cast (Nat.add_assoc ..) (castAdd p (natAdd m i)) := rfl
+
+theorem natAdd_natAdd (m n : Nat) {p : Nat} (i : Fin p) :
+    natAdd m (natAdd n i) = cast (Nat.add_assoc ..) (natAdd (m + n) i) :=
+  ext <| (Nat.add_assoc ..).symm
+
+@[simp]
+theorem cast_natAdd_zero {n n' : Nat} (i : Fin n) (h : 0 + n = n') :
+    cast h (natAdd 0 i) = cast ((Nat.zero_add _).symm.trans h) i :=
+  ext <| Nat.zero_add _
+
+@[simp]
+theorem cast_natAdd (n : Nat) {m : Nat} (i : Fin m) :
+    cast (Nat.add_comm ..) (natAdd n i) = addNat i n := ext <| Nat.add_comm ..
+
+@[simp]
+theorem cast_addNat {n : Nat} (m : Nat) (i : Fin n) :
+    cast (Nat.add_comm ..) (addNat i m) = natAdd m i := ext <| Nat.add_comm ..
+
+@[simp] theorem natAdd_last {m n : Nat} : natAdd n (last m) = last (n + m) := rfl
+
+theorem natAdd_castSucc {m n : Nat} {i : Fin m} : natAdd n (castSucc i) = castSucc (natAdd n i) :=
+  rfl
+
+theorem rev_castAdd (k : Fin n) (m : Nat) : rev (castAdd m k) = addNat (rev k) m := ext <| by
+  rw [val_rev, coe_castAdd, coe_addNat, val_rev, Nat.sub_add_comm (Nat.succ_le_of_lt k.is_lt)]
+
+theorem rev_addNat (k : Fin n) (m : Nat) : rev (addNat k m) = castAdd m (rev k) := by
+  rw [← rev_rev (castAdd ..), rev_castAdd, rev_rev]
+
+theorem rev_castSucc (k : Fin n) : rev (castSucc k) = succ (rev k) := k.rev_castAdd 1
+
+theorem rev_succ (k : Fin n) : rev (succ k) = castSucc (rev k) := k.rev_addNat 1
+
+/-! ### pred -/
+
+@[simp] theorem coe_pred (j : Fin (n + 1)) (h : j ≠ 0) : (j.pred h : Nat) = j - 1 := rfl
+
+@[simp] theorem succ_pred : ∀ (i : Fin (n + 1)) (h : i ≠ 0), (i.pred h).succ = i
+  | ⟨0, h⟩, hi => by simp only [mk_zero, ne_eq, not_true] at hi
+  | ⟨n + 1, h⟩, hi => rfl
+
+@[simp]
+theorem pred_succ (i : Fin n) {h : i.succ ≠ 0} : i.succ.pred h = i := by
+  cases i
+  rfl
+
+theorem pred_eq_iff_eq_succ {n : Nat} (i : Fin (n + 1)) (hi : i ≠ 0) (j : Fin n) :
+    i.pred hi = j ↔ i = j.succ :=
+  ⟨fun h => by simp only [← h, Fin.succ_pred], fun h => by simp only [h, Fin.pred_succ]⟩
+
+theorem pred_mk_succ (i : Nat) (h : i < n + 1) :
+    Fin.pred ⟨i + 1, Nat.add_lt_add_right h 1⟩ (ne_of_val_ne (Nat.ne_of_gt (mk_succ_pos i h))) =
+      ⟨i, h⟩ := by
+  simp only [ext_iff, coe_pred, Nat.add_sub_cancel]
+
+@[simp] theorem pred_mk_succ' (i : Nat) (h₁ : i + 1 < n + 1 + 1) (h₂) :
+    Fin.pred ⟨i + 1, h₁⟩ h₂ = ⟨i, Nat.lt_of_succ_lt_succ h₁⟩ := pred_mk_succ i _
+
+-- This is not a simp theorem by default, because `pred_mk_succ` is nicer when it applies.
+theorem pred_mk {n : Nat} (i : Nat) (h : i < n + 1) (w) : Fin.pred ⟨i, h⟩ w =
+    ⟨i - 1, Nat.sub_lt_right_of_lt_add (Nat.pos_iff_ne_zero.2 (Fin.val_ne_of_ne w)) h⟩ :=
+  rfl
+
+@[simp] theorem pred_le_pred_iff {n : Nat} {a b : Fin n.succ} {ha : a ≠ 0} {hb : b ≠ 0} :
+    a.pred ha ≤ b.pred hb ↔ a ≤ b := by rw [← succ_le_succ_iff, succ_pred, succ_pred]
+
+@[simp] theorem pred_lt_pred_iff {n : Nat} {a b : Fin n.succ} {ha : a ≠ 0} {hb : b ≠ 0} :
+    a.pred ha < b.pred hb ↔ a < b := by rw [← succ_lt_succ_iff, succ_pred, succ_pred]
+
+@[simp] theorem pred_inj :
+    ∀ {a b : Fin (n + 1)} {ha : a ≠ 0} {hb : b ≠ 0}, a.pred ha = b.pred hb ↔ a = b
+  | ⟨0, _⟩, _, ha, _ => by simp only [mk_zero, ne_eq, not_true] at ha
+  | ⟨i + 1, _⟩, ⟨0, _⟩, _, hb => by simp only [mk_zero, ne_eq, not_true] at hb
+  | ⟨i + 1, hi⟩, ⟨j + 1, hj⟩, ha, hb => by simp [ext_iff]
+
+@[simp] theorem pred_one {n : Nat} :
+    Fin.pred (1 : Fin (n + 2)) (Ne.symm (Fin.ne_of_lt one_pos)) = 0 := rfl
+
+theorem pred_add_one (i : Fin (n + 2)) (h : (i : Nat) < n + 1) :
+    pred (i + 1) (Fin.ne_of_gt (add_one_pos _ (lt_def.2 h))) = castLT i h := by
+  rw [ext_iff, coe_pred, coe_castLT, val_add, val_one, Nat.mod_eq_of_lt, Nat.add_sub_cancel]
+  exact Nat.add_lt_add_right h 1
+
+@[simp] theorem coe_subNat (i : Fin (n + m)) (h : m ≤ i) : (i.subNat m h : Nat) = i - m := rfl
+
+@[simp] theorem subNat_mk {i : Nat} (h₁ : i < n + m) (h₂ : m ≤ i) :
+    subNat m ⟨i, h₁⟩ h₂ = ⟨i - m, Nat.sub_lt_right_of_lt_add h₂ h₁⟩ := rfl
+
+@[simp] theorem pred_castSucc_succ (i : Fin n) :
+    pred (castSucc i.succ) (Fin.ne_of_gt (castSucc_pos i.succ_pos)) = castSucc i := rfl
+
+@[simp] theorem addNat_subNat {i : Fin (n + m)} (h : m ≤ i) : addNat (subNat m i h) m = i :=
+  ext <| Nat.sub_add_cancel h
+
+@[simp] theorem subNat_addNat (i : Fin n) (m : Nat) (h : m ≤ addNat i m := le_coe_addNat m i) :
+    subNat m (addNat i m) h = i := ext <| Nat.add_sub_cancel i m
+
+@[simp] theorem natAdd_subNat_cast {i : Fin (n + m)} (h : n ≤ i) :
+    natAdd n (subNat n (cast (Nat.add_comm ..) i) h) = i := by simp [← cast_addNat]; rfl
+
+/-! ### recursion and induction principles -/
+
+/-- Define `motive n i` by induction on `i : Fin n` interpreted as `(0 : Fin (n - i)).succ.succ…`.
+This function has two arguments: `zero n` defines `0`-th element `motive (n+1) 0` of an
+`(n+1)`-tuple, and `succ n i` defines `(i+1)`-st element of `(n+1)`-tuple based on `n`, `i`, and
+`i`-th element of `n`-tuple. -/
+-- FIXME: Performance review
+@[elab_as_elim] def succRec {motive : ∀ n, Fin n → Sort _}
+    (zero : ∀ n, motive n.succ (0 : Fin (n + 1)))
+    (succ : ∀ n i, motive n i → motive n.succ i.succ) : ∀ {n : Nat} (i : Fin n), motive n i
+  | 0, i => i.elim0
+  | Nat.succ n, ⟨0, _⟩ => by rw [mk_zero]; exact zero n
+  | Nat.succ _, ⟨Nat.succ i, h⟩ => succ _ _ (succRec zero succ ⟨i, Nat.lt_of_succ_lt_succ h⟩)
+
+/-- Define `motive n i` by induction on `i : Fin n` interpreted as `(0 : Fin (n - i)).succ.succ…`.
+This function has two arguments:
+`zero n` defines the `0`-th element `motive (n+1) 0` of an `(n+1)`-tuple, and
+`succ n i` defines the `(i+1)`-st element of an `(n+1)`-tuple based on `n`, `i`,
+and the `i`-th element of an `n`-tuple.
+
+A version of `Fin.succRec` taking `i : Fin n` as the first argument. -/
+-- FIXME: Performance review
+@[elab_as_elim] def succRecOn {n : Nat} (i : Fin n) {motive : ∀ n, Fin n → Sort _}
+    (zero : ∀ n, motive (n + 1) 0) (succ : ∀ n i, motive n i → motive (Nat.succ n) i.succ) :
+    motive n i := i.succRec zero succ
+
+@[simp] theorem succRecOn_zero {motive : ∀ n, Fin n → Sort _} {zero succ} (n) :
+    @Fin.succRecOn (n + 1) 0 motive zero succ = zero n := by
+  cases n <;> rfl
+
+@[simp] theorem succRecOn_succ {motive : ∀ n, Fin n → Sort _} {zero succ} {n} (i : Fin n) :
+    @Fin.succRecOn (n + 1) i.succ motive zero succ = succ n i (Fin.succRecOn i zero succ) := by
+  cases i; rfl
+
+/-- Define `motive i` by induction on `i : Fin (n + 1)` via induction on the underlying `Nat` value.
+This function has two arguments: `zero` handles the base case on `motive 0`,
+and `succ` defines the inductive step using `motive i.castSucc`.
+-/
+-- FIXME: Performance review
+@[elab_as_elim] def induction {motive : Fin (n + 1) → Sort _} (zero : motive 0)
+    (succ : ∀ i : Fin n, motive (castSucc i) → motive i.succ) :
+    ∀ i : Fin (n + 1), motive i
+  | ⟨0, hi⟩ => by rwa [Fin.mk_zero]
+  | ⟨i+1, hi⟩ => succ ⟨i, Nat.lt_of_succ_lt_succ hi⟩ (induction zero succ ⟨i, Nat.lt_of_succ_lt hi⟩)
+
+@[simp] theorem induction_zero {motive : Fin (n + 1) → Sort _} (zero : motive 0)
+    (hs : ∀ i : Fin n, motive (castSucc i) → motive i.succ) :
+    (induction zero hs : ∀ i : Fin (n + 1), motive i) 0 = zero := rfl
+
+@[simp] theorem induction_succ {motive : Fin (n + 1) → Sort _} (zero : motive 0)
+    (succ : ∀ i : Fin n, motive (castSucc i) → motive i.succ) (i : Fin n) :
+    induction (motive := motive) zero succ i.succ = succ i (induction zero succ (castSucc i)) := rfl
+
+/-- Define `motive i` by induction on `i : Fin (n + 1)` via induction on the underlying `Nat` value.
+This function has two arguments: `zero` handles the base case on `motive 0`,
+and `succ` defines the inductive step using `motive i.castSucc`.
+
+A version of `Fin.induction` taking `i : Fin (n + 1)` as the first argument.
+-/
+-- FIXME: Performance review
+@[elab_as_elim] def inductionOn (i : Fin (n + 1)) {motive : Fin (n + 1) → Sort _} (zero : motive 0)
+    (succ : ∀ i : Fin n, motive (castSucc i) → motive i.succ) : motive i := induction zero succ i
+
+/-- Define `f : Π i : Fin n.succ, motive i` by separately handling the cases `i = 0` and
+`i = j.succ`, `j : Fin n`. -/
+@[elab_as_elim] def cases {motive : Fin (n + 1) → Sort _}
+    (zero : motive 0) (succ : ∀ i : Fin n, motive i.succ) :
+    ∀ i : Fin (n + 1), motive i := induction zero fun i _ => succ i
+
+@[simp] theorem cases_zero {n} {motive : Fin (n + 1) → Sort _} {zero succ} :
+    @Fin.cases n motive zero succ 0 = zero := rfl
+
+@[simp] theorem cases_succ {n} {motive : Fin (n + 1) → Sort _} {zero succ} (i : Fin n) :
+    @Fin.cases n motive zero succ i.succ = succ i := rfl
+
+@[simp] theorem cases_succ' {n} {motive : Fin (n + 1) → Sort _} {zero succ}
+    {i : Nat} (h : i + 1 < n + 1) :
+    @Fin.cases n motive zero succ ⟨i.succ, h⟩ = succ ⟨i, Nat.lt_of_succ_lt_succ h⟩ := rfl
+
+theorem forall_fin_succ {P : Fin (n + 1) → Prop} : (∀ i, P i) ↔ P 0 ∧ ∀ i : Fin n, P i.succ :=
+  ⟨fun H => ⟨H 0, fun _ => H _⟩, fun ⟨H0, H1⟩ i => Fin.cases H0 H1 i⟩
+
+theorem exists_fin_succ {P : Fin (n + 1) → Prop} : (∃ i, P i) ↔ P 0 ∨ ∃ i : Fin n, P i.succ :=
+  ⟨fun ⟨i, h⟩ => Fin.cases Or.inl (fun i hi => Or.inr ⟨i, hi⟩) i h, fun h =>
+    (h.elim fun h => ⟨0, h⟩) fun ⟨i, hi⟩ => ⟨i.succ, hi⟩⟩
+
+theorem forall_fin_one {p : Fin 1 → Prop} : (∀ i, p i) ↔ p 0 :=
+  ⟨fun h => h _, fun h i => Subsingleton.elim i 0 ▸ h⟩
+
+theorem exists_fin_one {p : Fin 1 → Prop} : (∃ i, p i) ↔ p 0 :=
+  ⟨fun ⟨i, h⟩ => Subsingleton.elim i 0 ▸ h, fun h => ⟨_, h⟩⟩
+
+theorem forall_fin_two {p : Fin 2 → Prop} : (∀ i, p i) ↔ p 0 ∧ p 1 :=
+  forall_fin_succ.trans <| and_congr_right fun _ => forall_fin_one
+
+theorem exists_fin_two {p : Fin 2 → Prop} : (∃ i, p i) ↔ p 0 ∨ p 1 :=
+  exists_fin_succ.trans <| or_congr_right exists_fin_one
+
+theorem fin_two_eq_of_eq_zero_iff : ∀ {a b : Fin 2}, (a = 0 ↔ b = 0) → a = b := by
+  simp only [forall_fin_two]; decide
+
+/--
+Define `motive i` by reverse induction on `i : Fin (n + 1)` via induction on the underlying `Nat`
+value. This function has two arguments: `last` handles the base case on `motive (Fin.last n)`,
+and `cast` defines the inductive step using `motive i.succ`, inducting downwards.
+-/
+@[elab_as_elim] def reverseInduction {motive : Fin (n + 1) → Sort _} (last : motive (Fin.last n))
+    (cast : ∀ i : Fin n, motive i.succ → motive (castSucc i)) (i : Fin (n + 1)) : motive i :=
+  if hi : i = Fin.last n then _root_.cast (congrArg motive hi.symm) last
+  else
+    let j : Fin n := ⟨i, Nat.lt_of_le_of_ne (Nat.le_of_lt_succ i.2) fun h => hi (Fin.ext h)⟩
+    cast _ (reverseInduction last cast j.succ)
+termination_by n + 1 - i
+decreasing_by decreasing_with
+  -- FIXME: we put the proof down here to avoid getting a dummy `have` in the definition
+  exact Nat.add_sub_add_right .. ▸ Nat.sub_lt_sub_left i.2 (Nat.lt_succ_self i)
+
+@[simp] theorem reverseInduction_last {n : Nat} {motive : Fin (n + 1) → Sort _} {zero succ} :
+    (reverseInduction zero succ (Fin.last n) : motive (Fin.last n)) = zero := by
+  rw [reverseInduction]; simp
+
+@[simp] theorem reverseInduction_castSucc {n : Nat} {motive : Fin (n + 1) → Sort _} {zero succ}
+    (i : Fin n) : reverseInduction (motive := motive) zero succ (castSucc i) =
+      succ i (reverseInduction zero succ i.succ) := by
+  rw [reverseInduction, dif_neg (Fin.ne_of_lt (Fin.castSucc_lt_last i))]; rfl
+
+/-- Define `f : Π i : Fin n.succ, motive i` by separately handling the cases `i = Fin.last n` and
+`i = j.castSucc`, `j : Fin n`. -/
+@[elab_as_elim] def lastCases {n : Nat} {motive : Fin (n + 1) → Sort _} (last : motive (Fin.last n))
+    (cast : ∀ i : Fin n, motive (castSucc i)) (i : Fin (n + 1)) : motive i :=
+  reverseInduction last (fun i _ => cast i) i
+
+@[simp] theorem lastCases_last {n : Nat} {motive : Fin (n + 1) → Sort _} {last cast} :
+    (Fin.lastCases last cast (Fin.last n) : motive (Fin.last n)) = last :=
+  reverseInduction_last ..
+
+@[simp] theorem lastCases_castSucc {n : Nat} {motive : Fin (n + 1) → Sort _} {last cast}
+    (i : Fin n) : (Fin.lastCases last cast (Fin.castSucc i) : motive (Fin.castSucc i)) = cast i :=
+  reverseInduction_castSucc ..
+
+/-- Define `f : Π i : Fin (m + n), motive i` by separately handling the cases `i = castAdd n i`,
+`j : Fin m` and `i = natAdd m j`, `j : Fin n`. -/
+@[elab_as_elim] def addCases {m n : Nat} {motive : Fin (m + n) → Sort u}
+    (left : ∀ i, motive (castAdd n i)) (right : ∀ i, motive (natAdd m i))
+    (i : Fin (m + n)) : motive i :=
+  if hi : (i : Nat) < m then (castAdd_castLT n i hi) ▸ (left (castLT i hi))
+  else (natAdd_subNat_cast (Nat.le_of_not_lt hi)) ▸ (right _)
+
+@[simp] theorem addCases_left {m n : Nat} {motive : Fin (m + n) → Sort _} {left right} (i : Fin m) :
+    addCases (motive := motive) left right (Fin.castAdd n i) = left i := by
+  rw [addCases, dif_pos (castAdd_lt _ _)]; rfl
+
+@[simp]
+theorem addCases_right {m n : Nat} {motive : Fin (m + n) → Sort _} {left right} (i : Fin n) :
+    addCases (motive := motive) left right (natAdd m i) = right i := by
+  have : ¬(natAdd m i : Nat) < m := Nat.not_lt.2 (le_coe_natAdd ..)
+  rw [addCases, dif_neg this]; exact eq_of_heq <| (eqRec_heq _ _).trans (by congr 1; simp)
+
+/-! ### add -/
+
+@[simp] theorem ofNat'_add (x : Nat) (lt : 0 < n) (y : Fin n) :
+    Fin.ofNat' x lt + y = Fin.ofNat' (x + y.val) lt := by
+  apply Fin.eq_of_val_eq
+  simp [Fin.ofNat', Fin.add_def]
+
+@[simp] theorem add_ofNat' (x : Fin n) (y : Nat) (lt : 0 < n) :
+    x + Fin.ofNat' y lt = Fin.ofNat' (x.val + y) lt := by
+  apply Fin.eq_of_val_eq
+  simp [Fin.ofNat', Fin.add_def]
+
+/-! ### sub -/
+
+protected theorem coe_sub (a b : Fin n) : ((a - b : Fin n) : Nat) = (a + (n - b)) % n := by
+  cases a; cases b; rfl
+
+@[simp] theorem ofNat'_sub (x : Nat) (lt : 0 < n) (y : Fin n) :
+    Fin.ofNat' x lt - y = Fin.ofNat' (x + (n - y.val)) lt := by
+  apply Fin.eq_of_val_eq
+  simp [Fin.ofNat', Fin.sub_def]
+
+@[simp] theorem sub_ofNat' (x : Fin n) (y : Nat) (lt : 0 < n) :
+    x - Fin.ofNat' y lt = Fin.ofNat' (x.val + (n - y % n)) lt := by
+  apply Fin.eq_of_val_eq
+  simp [Fin.ofNat', Fin.sub_def]
+
+private theorem _root_.Nat.mod_eq_sub_of_lt_two_mul {x n} (h₁ : n ≤ x) (h₂ : x < 2 * n) :
+    x % n = x - n := by
+  rw [Nat.mod_eq, if_pos (by omega), Nat.mod_eq_of_lt (by omega)]
+
+theorem coe_sub_iff_le {a b : Fin n} : (↑(a - b) : Nat) = a - b ↔ b ≤ a := by
+  rw [sub_def, le_def]
+  dsimp only
+  if h : n ≤ a + (n - b) then
+    rw [Nat.mod_eq_sub_of_lt_two_mul h]
+    all_goals omega
+  else
+    rw [Nat.mod_eq_of_lt]
+    all_goals omega
+
+theorem coe_sub_iff_lt {a b : Fin n} : (↑(a - b) : Nat) = n + a - b ↔ a < b := by
+  rw [sub_def, lt_def]
+  dsimp only
+  if h : n ≤ a + (n - b) then
+    rw [Nat.mod_eq_sub_of_lt_two_mul h]
+    all_goals omega
+  else
+    rw [Nat.mod_eq_of_lt]
+    all_goals omega
+
+/-! ### mul -/
+
+theorem val_mul {n : Nat} : ∀ a b : Fin n, (a * b).val = a.val * b.val % n
+  | ⟨_, _⟩, ⟨_, _⟩ => rfl
+
+theorem coe_mul {n : Nat} : ∀ a b : Fin n, ((a * b : Fin n) : Nat) = a * b % n
+  | ⟨_, _⟩, ⟨_, _⟩ => rfl
+
+protected theorem mul_one (k : Fin (n + 1)) : k * 1 = k := by
+  match n with
+  | 0 => exact Subsingleton.elim (α := Fin 1) ..
+  | n+1 => simp [ext_iff, mul_def, Nat.mod_eq_of_lt (is_lt k)]
+
+protected theorem mul_comm (a b : Fin n) : a * b = b * a :=
+  ext <| by rw [mul_def, mul_def, Nat.mul_comm]
+
+protected theorem mul_assoc (a b c : Fin n) : a * b * c = a * (b * c) := by
+  apply eq_of_val_eq
+  simp only [val_mul]
+  rw [← Nat.mod_eq_of_lt a.isLt, ← Nat.mod_eq_of_lt b.isLt, ← Nat.mod_eq_of_lt c.isLt]
+  simp only [← Nat.mul_mod, Nat.mul_assoc]
+
+protected theorem one_mul (k : Fin (n + 1)) : (1 : Fin (n + 1)) * k = k := by
+  rw [Fin.mul_comm, Fin.mul_one]
+
+protected theorem mul_zero (k : Fin (n + 1)) : k * 0 = 0 := by simp [ext_iff, mul_def]
+
+protected theorem zero_mul (k : Fin (n + 1)) : (0 : Fin (n + 1)) * k = 0 := by
+  simp [ext_iff, mul_def]
+
+end Fin
+
+namespace USize
+
+@[simp] theorem lt_def {a b : USize} : a < b ↔ a.toNat < b.toNat := .rfl
+
+@[simp] theorem le_def {a b : USize} : a ≤ b ↔ a.toNat ≤ b.toNat := .rfl
+
+@[simp] theorem zero_toNat : (0 : USize).toNat = 0 := Nat.zero_mod _
+
+@[simp] theorem mod_toNat (a b : USize) : (a % b).toNat = a.toNat % b.toNat :=
+  Fin.mod_val ..
+
+@[simp] theorem div_toNat (a b : USize) : (a / b).toNat = a.toNat / b.toNat :=
+  Fin.div_val ..
+
+@[simp] theorem modn_toNat (a : USize) (b : Nat) : (a.modn b).toNat = a.toNat % b :=
+  Fin.modn_val ..
+
+theorem mod_lt (a b : USize) (h : 0 < b) : a % b < b := USize.modn_lt _ (by simp at h; exact h)
+
+theorem toNat.inj : ∀ {a b : USize}, a.toNat = b.toNat → a = b
+  | ⟨_, _⟩, ⟨_, _⟩, rfl => rfl
+
+end USize

src/Init/Data/Float.lean

@@ -26,6 +26,8 @@ opaque floatSpec : FloatSpec := {
   decLe := fun _ _ => inferInstanceAs (Decidable True)
 }
 
+/-- Native floating point type, corresponding to the IEEE 754 *binary64* format
+(`double` in C or `f64` in Rust). -/
 structure Float where
   val : floatSpec.float
 
@@ -132,7 +134,7 @@ instance : ReprAtom Float  := ⟨⟩
 @[extern "round"] opaque Float.round : Float → Float
 @[extern "fabs"] opaque Float.abs : Float → Float
 
-instance : Pow Float Float := ⟨Float.pow⟩
+instance : HomogeneousPow Float := ⟨Float.pow⟩
 
 instance : Min Float := minOfLe
 

src/Init/Data/Format/Basic.lean

@@ -300,11 +300,18 @@ instance : MonadPrettyFormat (StateM State) where
   startTag _         := return ()
   endTags _          := return ()
 
-/-- Pretty-print a `Format` object as a string with expected width `w`. -/
+/--
+Renders a `Format` to a string.
+* `width`: the total width
+* `indent`: the initial indentation to use for wrapped lines
+  (subsequent wrapping may increase the indentation)
+* `column`: begin the first line wrap `column` characters earlier than usual
+  (this is useful when the output String will be printed starting at `column`)
+-/
 @[export lean_format_pretty]
-def pretty (f : Format) (w : Nat := defWidth) : String :=
-  let act: StateM State Unit := prettyM f w
-  act {} |>.snd.out
+def pretty (f : Format) (width : Nat := defWidth) (indent : Nat := 0) (column := 0) : String :=
+  let act : StateM State Unit := prettyM f width indent
+  State.out <| act (State.mk "" column) |>.snd
 
 end Format
 

src/Init/Data/Int.lean

@@ -5,3 +5,10 @@ Authors: Leonardo de Moura
 -/
 prelude
 import Init.Data.Int.Basic
+import Init.Data.Int.Bitwise
+import Init.Data.Int.DivMod
+import Init.Data.Int.DivModLemmas
+import Init.Data.Int.Gcd
+import Init.Data.Int.Lemmas
+import Init.Data.Int.Order
+import Init.Data.Int.Pow